JP6032591B2 - Method for producing silica nano hollow particles - Google Patents

Description

The present invention relates to a method for producing nano hollow particles comprising silica shells.

In recent years, hollow bodies called microcapsules have attracted attention. For example, in the field of medicine and cosmetics, in addition to sustained-release medicines and sustained-release cosmetics encapsulating active ingredients inside hollow bodies, protection of substances that degrade or deteriorate due to contact with the external environment, drug delivery systems Research has been actively conducted to utilize a hollow body (microcapsule) as a carrier for the purpose. In the papermaking field, hollow bodies (microcapsules) containing dyes are used for pressure-sensitive paper. In addition to this, the hollow body is expected to be applied in many fields, such as its use as a lightweight filler, and various studies have been made on its production.
In recent years, as part of nanotechnology research, application research on particles having a particle size of several hundred nm or less has been actively conducted, and nano-sized hollow particles are also desired.

Here, as a technique related to hollow particles, particularly siliceous hollow particles, for example, in Patent Document 1, a hollow silica powder is obtained by hydrolyzing after mixing and spraying an organic silicon compound such as methoxysilicate and ethoxysilicate and a foaming agent. It is described that it is obtained. In Patent Document 2, alcohol, water, and an acid catalyst are added to tetraethyl orthosilicate to cause partial hydrolysis, and then dibutyl phthalate is added, and this solution is added to an aqueous ammonia solution containing a surfactant. Has been proposed to produce spherical and hollow porous silica particles by mixing and stirring, emulsifying and polycondensation reaction.

Furthermore, in Patent Document 3, micron-sized spherical silica synthesized by hydrolysis and polycondensation reaction caused by tetraalkoxysilane and water, and the shell constituting the silica particles is denser on the outer side and closer to the inner side. Micron-sized hollow spherical silica particles having a coarse concentration gradient structure have been proposed. In Patent Document 4, hollow silica particles composed of a dense silica shell are obtained by precipitating active silica on a support other than silica from an alkali metal silicate under specific conditions, and then removing the support. A manufacturing method has also been proposed.

Among these, the techniques described in Patent Documents 1 to 3 utilize a so-called interfacial reaction in which silica is precipitated at the gas-liquid or liquid-liquid (aqueous phase-oil phase) interface. The silica hollow particles to be obtained are spherical and have a particle size of micron order or larger, and hollow particles of sub-micron order to nano order cannot be obtained. Moreover, although it is described in Patent Document 4 that hollow silica particles of 20 nm or more can be produced, according to the experiments of the present inventors, the aggregation becomes intense when it becomes nano order, and as a result, it becomes micron order. It has been confirmed that it becomes aggregated particles. Further, in Patent Document 4, the silica shell constituting the hollow particle is formed by agglomeration of silica fine particles, and as a result, the silica shell is fine but has fine pores. They have confirmed.

In view of such a situation, in developing nano-sized hollow particles, the present inventors wanted to have a controlled dispersion and good dispersibility in order to more effectively express the nano-sized features. As a result of diligent research focusing on the need for technology for controlling the properties of the shells constituting the hollow particles, particularly pores at the molecular size, as described in Patent Document 5, Successful development of hollow particles.

The highly dispersible silica nanohollow particles described in Patent Document 5 are nanohollow particles composed of a dense silica shell, and the primary particle diameter by transmission electron microscopy is 30 to 300 nm, and the particle diameter by dynamic light scattering is 30. It is ˜800 nm, and pores of 2 to 20 nm are not detected in the pore distribution measured by mercury porosimetry or gas adsorption method. And the silica nano hollow particle described in Patent Document 5 is prepared by using calcium carbonate in a water-containing cake state and using this as a core, and dispersing the water-containing cake state calcium carbonate core in alcohol, and adding silicon alkoxide or the like to it. It is manufactured by coating silica by adding, and then dissolving and removing calcium carbonate as a core by acid treatment.

However, the silica coating using the ammonium hydroxide (NH ₄ OH) catalyst in Patent Document 5 is slow in the hydrolysis of silicon alkoxide and the subsequent condensation reaction, so that a low-strength silica shell is formed. There was a problem that the silica shell was broken by impact when dissolving and removing the core of the particles. On the other hand, increasing the amount of NH ₄ OH catalyst or increasing the reaction time to silica-coated increases the strength of the silica shell, but generates a large amount of solid particles and loses the homogeneity of the nano hollow particles. There was a problem.

JP-A-6-91194 Japanese Patent No. 2590428 Japanese Patent Laid-Open No. 11-29318 Japanese Patent No. 3419787 Japanese Patent No. 4654428

An object of the present invention is to solve such problems of the prior art, and to solve such problems, and has a dense silica shell with little aggregation to secondary particles. It is providing the manufacturing method which obtains a nano hollow particle in a short time.

  The present inventors have found that the above problem can be solved by selecting a catalyst for silica coating. That is, according to the present invention, the following method is provided.

[1] In the presence of silicon alkoxide, an organic solvent, distilled water, and a catalyst, a silica shell is formed on a powder surface in a dry powder state or a suspension state having a predetermined size and shape to form silica-coated particles, and then the silica a method of manufacturing a hollow nanoparticles comprising from the inside of the silica powder shell made by removing the coated particles, wherein the catalyst ammonium (NH ₄₎ ions, hydrogen (H) ions, sodium (Na) ions, potassium (K) and one cation ion, a combination of a fluoride (F) ions, tetrafluoroborate (BF ₄₎ anion or anions of emissions, spherical, spheroid or cubic It is characterized by having a silica shell.

[2] the compound of the catalyst, ammonium fluoride _(NH 4 F), hydrogen fluoride (HF), potassium fluoride (KF), ammonium tetrafluoroborate _(NH 4 _BF 4), f hexafluorobutene sodium borate It is any one of (NaBF ₄ ) .

[3] The thickness of the silica shell of the nano hollow particles, characterized in that it is a 2Nm～25nm.

2 is an electron microscope (TEM) photograph of silica-shell nanosilica hollow particles produced under the conditions of Example 2. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

The method for producing nano hollow particles comprising silica shells of the present invention comprises adding a compound serving as a catalyst to a mixture of silicon alkoxide, organic solvent, and distilled water, and particles such as calcium carbonate serving as a core in the presence of the catalyst. The surface is coated with silica. Thereafter, the core such as calcium carbonate is removed with an acid or the like to obtain nano hollow particles made of silica shells.

Any silicon alkoxide can be used as long as it can precipitate silica by hydrolysis. Examples thereof include tetraethoxysilane, trimethoxysilane, tetramethoxysilane, triethoxysilane, tripropoxysilane, tetrapropoxysilane, and tributoxysilane. Tributoxysilane or the like can be used.

Here, the organic solvent is not particularly limited as long as it is soluble in silicon alkoxide and water and can further promote hydrolysis of silicon alkoxide, such as alcohols, glycols, glycol esters, acetone and the like. Examples include simple solvents such as ketones, aliphatic carbons, and aromatic hydrocarbons, or a mixed solvent of two or more of these. Among these, alcohols are preferable.

Catalysts include ammonium (NH ₄ ) ion, hydrogen (H) ion, lithium (Li) ion, sodium (Na) ion, potassium (K) ion, fluoride (F) ion, tetra fluoroborate (BF ₄₎ anion, the combination of hexafluorophosphate (PF ₆₎ anion or anions of emissions are preferred. Among these, any cation of ammonium (NH ₄ ) ion, hydrogen (H) ion, sodium (Na) ion, potassium (K) ion, fluoride (F) ion, tetrafluoroboric acid (BF ₄ ) A combination of any anions of anions is particularly preferred.

Therefore, the compounds serving as catalysts include ammonium fluoride (NH ₄ F), hydrogen fluoride (HF), sodium fluoride (NaF), potassium fluoride (KF), and ammonium tetrafluoroborate (NH ₄ BF ₄ ). , Tetrafluoroboric acid (HBF ₄ ), sodium tetrafluoroborate (NaBF ₄ ), potassium tetrafluoroborate (KBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), sodium hexafluorophosphate (NaPF ₆ ), An example is potassium hexafluorophosphate (KPF ₆ ).

The nano hollow particles made of the silica shell obtained by the present invention are in the form of a sphere, a spheroid or a cube. Here, “spherical” means not only a sphere but also a shape similar to a sphere surrounded by a surface, and “spheroid” means not only a spheroid but also a spheroid surrounded by a surface. It refers to a similar shape, and the “cubic shape” is not limited to a cube, but a shape similar to a cube surrounded by a face. The hollow particles made of silica shells having such a spherical shape, spheroid shape, or cubic shape are, for example, calcium carbonate particles, polystyrene, etc. in the form of a spherical shape, spheroid shape, or cubic shape in a dry powder state. The polymer material is used as a core material. The removal of the core material after the formation of the silica shell is performed by acid treatment or heating. The average particle diameter of the hollow particles is the average of the major axis and the minor axis in the case of a spheroid, and the length of one side in the case of a cube. In addition, it is preferable that the thickness of the silica shell of the nano hollow particle made of the silica shell is 2 nm to 25 nm from the viewpoint of maintaining the strength of the hollow structure.

EXAMPLES Hereinafter, although this invention is further demonstrated based on an Example, this invention is not limited to these Examples.

Silica core particles were produced by dispersing a predetermined amount of cubic or spherical core particles in an ethanol solvent, adding predetermined amounts of silicon alkoxide (TEOS), distilled water, and each catalyst and reacting at room temperature for a predetermined time. When polystyrene (PS) was used as the core particles, the core particles were removed by thermal decomposition by heating to obtain silica nano hollow particles. When calcium carbonate (CaCO ₃ , CC for short) was used as the core particle, the core particle was dissolved and removed using a diluted hydrochloric acid aqueous solution, and the residue was removed and washed to obtain silica nano hollow particles.

As a catalyst, potassium fluoride (KF), ammonium fluoride (NH ₄ F), hydrogen fluoride (HF), ammonium tetrafluoroborate (NH ₄ BF ₄ ), and ammonium hydroxide (NH ₄ OH) as a comparative example Was used. The reaction time using each catalyst was evaluated as follows. After the addition of TEOS, distilled water, and catalyst to the core particle / organic solvent dispersion, the core particles are removed from the dispersion using a membrane filter after a predetermined time, and the amount of unreacted TEOS remaining in the filtrate is analyzed by X-ray fluorescence (XRF, EDX-720, manufactured by Shimadzu Corporation). The time when the amount of unreacted TEOS was not detected was defined as the reaction time of the catalyst. Table 1 shows the reaction conditions and reaction times of Examples 1 to 7 and Comparative Examples 1 and 2. The electron micrograph of the silica nano hollow particle manufactured on the conditions of Example 2 in FIG. 1 is shown.

Compared with Examples 1-7, the reaction time of the comparative examples 1 and 2 is 10 times or more longer, and the difference in reaction rate is clear. In addition, as for the hollow particle which consists of a silica shell of Examples 1-7, all had an average particle diameter of 50-500 nm, and the shell thickness was 5-20 nm. Further, in the pore distribution measured by the mercury intrusion method or the gas adsorption method, pores of 2 to 20 nm are not detected, and the silica shell is considered to be dense.

Claims (3)

In the presence of silicon alkoxide, an organic solvent, distilled water, and a catalyst, a silica shell is formed on the surface of a powder in a dry powder state or a suspension state having a predetermined size and shape to form silica-coated particles. a method of manufacturing a hollow nanoparticles comprising silica shells made by removing the powder inside, the catalyst is ammonium (NH ₄₎ ions, hydrogen (H) ions, sodium (Na) ions, potassium (K) and any cation ion, fluoride (F) ions, a combination of a tetrafluoroborate (BF ₄₎ anion or anions of emissions, spherical, spheroid or silica is a cube-shaped A method for producing nano hollow particles comprising shells. Compounds of the catalyst, ammonium fluoride _(NH 4 F), hydrogen fluoride (HF), potassium full Tsu reduction (KF), ammonium tetrafluoroborate _(NH 4 _BF 4), f hexafluorobutene sodium borate (NaBF method for producing hollow nanoparticles of silica shell of any der Ru請 Motomeko 1 wherein _4). Before cinchona Bruno thickness of the silica shell of the hollow particles, method for producing the hollow nanoparticles of silica shell of claim 1 or claim 2 wherein the 2Nm～25nm.