JP7798810B2 - Metal-containing colloidal silica and its manufacturing method - Google Patents

Description

The present invention relates to metal-containing colloidal silica in which the surface of colloidal silica is modified with a metal, and a method for producing the same.

Colloidal silica has traditionally been used in a variety of applications, including as a catalyst carrier, chromatography filler, silica glass, resin filler, abrasive composition, adhesive binder for phosphors in cathode ray tube manufacturing, gelling agent, thixotropic agent, and shatterproofing agent for electrolyte in batteries, inorganic adhesives, and paints.

Technology for supporting metals on the surface of silica particles is known in order to impart properties suitable for these applications. For example, Patent Document 1 proposes a method for using metal fine particles supported on the surface of silica particles by plasma treatment, rather than using metal fine particles themselves, in order to achieve lightness, dispersibility, cost, etc. Patent Document 2 describes that, as a result of investigating ways to improve the polishing rate and surface smoothness of colloidal silica for polishing applications, this goal was achieved by using metal-supported silica particles. Other technologies related to colloidal silica using silica particles supported, coated, or containing metals have also been disclosed (see, for example, Patent Documents 3 to 10).

Generally, colloidal silica has a particle size of around 5 to 300 nm. However, when it comes to the microscopic range of 100 nm or less, from the perspective of modifying colloidal silica with metal microparticles, the metal microparticles must be made even smaller. Furthermore, the influence of the metal microparticles causes silica particles to aggregate, making it difficult to obtain colloidal silica modified with metal.

JP 2014-152079 A JP 2015-193486 A Japanese Unexamined Patent Publication No. 2-292201 Japanese Patent Application Publication No. 4-210606 Japanese Patent Application Publication No. 4-310235 Japanese Patent Application Publication No. 8-253310 Japanese Patent Application Laid-Open No. 2001-130910 Japanese Patent Application Laid-Open No. 2005-119909 Japanese Patent Application Laid-Open No. 2006-306708 Special Publication No. 2010-505734

The modification of colloidal silica with metals using the above-mentioned conventional technology is a method in which a metal compound is reacted with silica particles to support or coat the silica particle surface with the metal to be modified, but the smaller the silica particles, the larger the specific surface area becomes, and a large amount of metal compound must be used to support the metal, which is inefficient. Furthermore, when considering that colloidal silica is used to disperse in base materials such as paints and films, it is required that the colloidal particles be stable over a long period of time.
Therefore, an object of the present invention is to provide a metal-containing colloidal silica in which colloidal particles are resistant to aggregation and which has excellent storage stability.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that by reacting activated silicic acid on the surface of metal-containing colloidal silica obtained by adding a metal salt compound during the particle growth process of silica particles to form a silica layer, the colloidal particles become less likely to aggregate, and thus completed the present invention.

That is, the present invention provides metal-containing colloidal silica having a mixed layer in which metal M is dispersed within silica, wherein the mixed layer is located between a core silica particle and a silica layer located on the surface of the metal-containing colloidal silica, wherein the metal M is one or more selected from Au, Ag, Cu, Zn, Ti, Pt, Mg, Zr, Fe, Sr, Ca, V, Mo, Bi, Nb, Ga, Ge, Sn, Ba, W, Co, Ni, and Mn, wherein the molar ratio of silicon to metal M (Si/M) in the coating layer comprising the mixed layer and the silica layer is 10 or more and 10,000 or less, and wherein the metal M is uniformly and finely dispersed within the mixed layer.

The present invention also relates to a method for producing metal-containing colloidal silica, comprising the steps of: (a) adding a metal salt compound to an aqueous solution of activated silicic acid to prepare an aqueous solution of activated silicic acid containing a metal salt compound; (b) reacting the aqueous solution of activated silicic acid containing the metal salt compound under alkaline conditions in the presence of colloidal silica to form a mixed layer on the surface of the colloidal silica, in which the metal is uniformly and finely dispersed within the silica; and (c) reacting the colloidal silica that has formed the mixed layer with an aqueous solution of activated silicic acid under alkaline conditions to form a silica layer on the surface of the mixed layer.

The present invention provides metal-containing colloidal silica with excellent storage stability and a method for producing the same.

1 is a TEM photograph of the silver-containing colloidal silica obtained in Example 1. 1 shows the results of elemental mapping by TEM-EDX of the silver-containing colloidal silica obtained in Example 1. 1 is an XPS spectrum of the silver-containing colloidal silica obtained in Example 1.

The metal-containing colloidal silica of the present invention has a mixed layer in which metal M is uniformly and finely dispersed within the silica, and this mixed layer is located between the core silica particle and the silica layer located on the surface of the metal-containing colloidal silica.

The silica particles serve as the core material for the metal-containing colloidal silica of the present invention and are coated with the mixed layer. The particle diameter of the silica particles may be large enough to maintain the colloidal state of the resulting metal-containing colloidal silica; for example, a diameter of 0.5 nm to 100 nm, preferably 1 nm to 50 nm, is preferred.

The mixed layer is composed of silica and metal M, and has a form in which metal M is uniformly and finely dispersed in silica.

The metal M is preferably one or more selected from Au, Ag, Cu, Zn, Ti, Pt, Mg, Zr, Fe, Sr, Ca, V, Mo, Bi, Nb, Ga, Ge, Sn, Ba, W, Co, Ni, and Mn, and can be selected appropriately depending on the application of the metal-containing colloidal silica. For example, when the metal-containing colloidal silica is used as an antibacterial agent, bactericide, antiviral agent, or viricide, the metal M is preferably one or more selected from Ag and Cu.

In this invention, "antibacterial" means inhibiting bacterial growth, and "sterilizing" means killing bacteria. Furthermore, "antiviral" and "viricidal" both mean inactivating viruses.

The metal M of the present invention may be either a simple metal or a metal compound. That is, the mixed layer of the metal-containing colloidal silica of the present invention has a form in which a simple metal is uniformly and finely dispersed in silica, a form in which a metal compound is uniformly and finely dispersed, or a form in which a simple metal and a metal compound are uniformly and finely dispersed.

The metal compound is preferably an oxide or hydroxide from the viewpoint of being easily finely dispersed and stably maintained in the silica of the mixed layer. For example, when the metal-containing colloidal silica of the present invention is used for an antibacterial agent, a bactericide, an antiviral agent, or a virucide, when the metal M is Ag, it is preferably finely dispersed in the mixed layer as metallic silver, silver oxide ( _Ag2O , AgO, _Ag2O3 ) and silver hydroxide ( _AgOH ), and when the metal M is Cu, it is preferably finely dispersed in the mixed layer as metallic copper, copper oxide (CuO, _Cu2O ) and copper hydroxide ( _Cu2O , Cu(OH) ₂ ).

In the present invention, "metal M is uniformly and finely dispersed in the mixed layer" means that "the presence of metal M is confirmed by elemental analysis of the metal-containing colloidal silica using X-ray photoelectron spectroscopy (XPS analysis), and the presence of metal M in the mixed layer is not confirmed in an elemental mapping image obtained by analyzing the metal-containing colloidal silica at 1,000,000 times magnification using transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX)." In other words, "metal M is uniformly and finely dispersed" means that metal M is dispersed at a size that cannot be detected with the resolution of TEM-EDX, and there are no areas where metal M aggregates.

The particle size of the metal-containing colloidal silica of the present invention can be a typical particle size of around 5 to 300 nm, as long as the silica particles can maintain a colloidal state. However, when used, for example, as an antibacterial, antiviral, bactericidal, or virucidal material, a particle size of 100 nm or less, close to the size of bacteria and viruses, will be more effective. From this perspective, it is preferable that the average particle size of the metal-containing colloidal silica of the present invention be 1 nm or more and 100 nm or less, and particularly 2 nm or more and 80 nm.

The mixed layer is made of silica containing a metal, and the molar ratio of silicon to metal M (Si/M) is preferably 5 to 5,000, more preferably 10 to 3,000, and even more preferably 50 to 1,000. If this molar ratio is less than 5, the colloidal silica becomes unstable, which can lead to the settling or gelation of silica particles. If it exceeds 5,000, the properties of the metal cannot be utilized.

By forming the mixed layer in which the metal is uniformly and finely dispersed within the silica, it is possible to prevent the metal from falling off the silica particles. Furthermore, because the surface of the silica particles is coated with the mixed layer, it is possible to efficiently modify the silica particles with a small amount of metal.

The thickness of the mixed layer is preferably 1 nm or more and 50 nm or less from the perspective of efficient modification and production of silica particles, and more preferably 1 nm or more and 10 nm or less.

The silica layer is located on the outer surface of the metal-containing colloidal silica of the present invention and covers the mixed layer. The thickness of the silica layer is preferably 0.5 nm to 10 nm, from the viewpoint of preventing the metal M from falling off while taking advantage of the properties of the metal M, such as antibacterial, bactericidal, antiviral, and virucidal properties, and is more preferably 1 nm to 5 nm.

The metal-containing colloidal silica of the present invention has a coating layer that is a combination of the mixed layer and the silica layer. The molar ratio of silicon to metal M (Si/M) in this coating layer that is a combination of the mixed layer and the silica layer is 10 to 10,000, preferably 20 to 8,000, and particularly preferably 50 to 5,000. If this molar ratio is less than 10, the colloidal silica becomes unstable, which can cause the silica particles to settle or gel. If it exceeds 10,000, the properties of the metal content cannot be utilized.

The molar ratio of silicon to metal M (Si/M) in the metal-containing colloidal silica of the present invention varies depending on the size of the silica particles that serve as the core material, but is preferably 10 to 20,000, more preferably 20 to 10,000, and particularly preferably 30 to 5,000. If this molar ratio is less than 10, the colloidal silica becomes unstable, which can lead to the settling or gelation of the silica particles. If it exceeds 20,000, the properties of the metal content cannot be utilized.

The method for producing metal-containing colloidal silica of the present invention comprises the steps of: (a) adding a metal salt compound to an aqueous solution of activated silicic acid to prepare an aqueous solution of activated silicic acid containing a metal salt compound; (b) reacting the aqueous solution of activated silicic acid containing the metal salt compound in the presence of colloidal silica under alkaline conditions to form a mixed layer on the surface of the colloidal silica, in which the metal is uniformly and finely dispersed within the silica; and (c) reacting the colloidal silica that has formed the mixed layer with the aqueous solution of activated silicic acid under alkaline conditions to form a silica layer on the surface of the mixed layer.

In step (a) of the present invention, an activated silica aqueous solution containing a metal salt compound is prepared, which will serve as the raw material for the mixed layer formed in step (b) described below.

The activated silica aqueous solution in step (a) is preferably obtained by contacting an alkali silicate aqueous solution with a cation exchange resin. The alkali silicate aqueous solution used as a raw material is preferably a sodium silicate aqueous solution known as water glass (water glass No. 1 to No. 4, etc.). Water glass is relatively inexpensive and easily available. The alkali silicate aqueous solution can be diluted with water as needed before use.

The cation exchange resin can be selected from known resins and is not particularly limited. The contacting step between the aqueous alkali silicate solution and the cation exchange resin can be carried out, for example, by diluting the aqueous alkali silicate solution with water to a silica concentration of 3 to 10% by weight, then contacting it with an H-type strongly acidic cation exchange resin to dealkalize it, and, if necessary, contacting it with an OH-type strongly basic anion exchange resin to deanionize it. This step produces activated silicic acid. Various detailed contact conditions have been proposed in the past, and any of these known conditions can be used in the present invention.

The metal salt compound used in step (a) is preferably at least one selected from nitrates, chlorides, acetates, phosphates, and sulfates. Furthermore, the metal in the metal salt compound is preferably one or more selected from Au, Ag, Cu, Zn, Ti, Pt, Mg, Zr, Fe, Sr, Ca, V, Mo, Bi, Nb, Ga, Ge, Sn, Ba, W, Co, Ni, and Mn, and can be selected appropriately depending on the application of the metal-containing colloidal silica.

The metal salt compound is preferably added to the activated silicic acid aqueous solution at a concentration such that the molar ratio of silicon to metal M (Si/M) in the resulting coating layer, which is the combined total of the mixed layer of metal-containing colloidal silica and the silica layer, is 10 to 10,000, preferably 20 to 8,000, and especially 50 to 5,000. In other words, the molar ratio of silicon to metal M (Si/M) in the resulting mixed layer of metal-containing colloidal silica is preferably 5 to 5,000, more preferably 10 to 3,000, and especially 50 to 1,000.

Next, a mixed layer is formed in step (b). In step (b), an alkaline agent is added to the activated silicic acid aqueous solution containing the metal salt compound in the presence of colloidal silica, the pH is adjusted to 8 or higher, and the solution is heated to 60-240°C, forming a mixed layer on the surface of the colloidal silica in which the metal is uniformly and finely dispersed within the silica.

As the alkaline agent, alkali metal hydroxides such as sodium hydroxide are the least expensive materials. If alkali metals are not preferred, nitrogen-containing organic alkaline compounds such as amines and quaternary ammonium hydroxides can be used. As amines, low-volatility tertiary amines such as triethanolamine, secondary amines such as piperazine, and aliphatic amines such as ethylenediamine can be used. As quaternary ammonium hydroxides, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and trimethyl-2-hydroxyethylammonium hydroxide (also known as choline hydroxide) can be used.

By using the nitrogen-containing organic alkali compound, the alkali metal content per silica can be reduced to 50 ppm or less. This level of alkali metal content is preferable for applications such as ceramics, catalyst binders, and abrasives for electronic materials. A content of 30 ppm or less is more preferable.

Colloidal silica prepared by ion exchange, for example, can be used as the colloidal silica. In the ion exchange colloidal silica production process, an aqueous solution of alkaline silicate is first diluted with water to a silica concentration of 3-10% by weight, then contacted with an H-type strongly acidic cation exchange resin for dealkalization, and optionally with an OH-type strongly basic anion exchange resin for deanionization, to produce activated silica. Various types of ion exchange resins and conditions have been proposed, and any of these known methods can be used. Next, an alkaline agent is added to achieve a pH of 8 or higher, as per standard methods, and the mixture is heated to 60-240°C to produce colloidal silica from the activated silica. Depending on the heating temperature, colloidal silica with a particle size of 5-300 nm can be obtained. Alternatively, commercially available colloidal silica can be used.

The mixed layer obtained by step (b) of the present invention is one in which metal M is uniformly and finely dispersed in silica.

The metal M is preferably one or more selected from Au, Ag, Cu, Zn, Ti, Pt, Mg, Zr, Fe, Sr, Ca, V, Mo, Bi, Nb, Ga, Ge, Sn, Ba, W, Co, Ni, and Mn, and can be selected appropriately depending on the application of the metal-containing colloidal silica. For example, when the metal-containing colloidal silica is used as an antibacterial agent, bactericide, antiviral agent, or viricide, the metal M is preferably one or more selected from Ag and Cu.

The metal M of the present invention may be either a simple metal or a metal compound. That is, the mixed layer of the metal-containing colloidal silica of the present invention has a form in which a simple metal is uniformly and finely dispersed in silica, a form in which a metal compound is uniformly and finely dispersed, or a form in which a simple metal and a metal compound are uniformly and finely dispersed.

The metal compound is preferably an oxide or hydroxide from the viewpoint of being easily finely dispersed and stably maintained in the silica of the mixed layer. For example, when the metal-containing colloidal silica of the present invention is used for an antibacterial agent, a bactericide, an antiviral agent, or a virucide, when the metal M is Ag, it is preferably finely dispersed in the mixed layer as metallic silver, silver oxide ( _Ag2O , AgO, _Ag2O3 ) and silver hydroxide ( _AgOH ), and when the metal M is Cu, it is preferably finely dispersed in the mixed layer as metallic copper, copper oxide (CuO, _Cu2O ) and copper hydroxide ( _Cu2O , Cu(OH) ₂ ).

The mixed layer is made of silica containing a metal, and the molar ratio of silicon to metal M (Si/M) is preferably 5 to 5,000, more preferably 10 to 3,000, and particularly preferably 50 to 1,000. If this molar ratio is less than 10, the colloidal silica becomes unstable, which can cause the silica particles to settle or gel. If it exceeds 5,000, the properties of the metal cannot be utilized.

By forming the mixed layer in which the metal is uniformly and finely dispersed within the silica, it is possible to prevent the metal from falling off the silica particles. Furthermore, because the surface of the silica particles is coated with the mixed layer, it is possible to efficiently modify the silica particles with a small amount of metal.

From the standpoint of manufacturing efficiency, the thickness of the mixed layer is preferably 1 nm or more and 50 nm or less, and more preferably 1 nm or more and 10 nm or less.

Next, a silica layer is formed in step (c). In step (c), an active silicic acid aqueous solution and an alkaline agent are added to the colloidal silica that has formed the mixed layer, the pH is adjusted to 8 or higher, and the mixture is heated to 60 to 240°C, forming a silica layer on the surface of the mixed layer.

The activated silicic acid aqueous solution can be the same as the activated silicic acid aqueous solution used in step (a). Furthermore, the alkaline agent can be the same as the alkaline agent used in step (b).

The amount of the activated silicic acid aqueous solution added is adjusted depending on the scale of the process, but from the standpoint of the storage stability of the resulting metal-containing colloidal silica, it is preferable to add it so that the thickness of the silica layer is 1 nm or more and 20 nm or less, particularly 1 nm or more and 10 nm or less.

The particle size of the metal-containing colloidal silica obtained by the manufacturing method of the present invention can be a typical particle size of around 5 to 300 nm, as long as the silica particles can maintain a colloidal state. However, when used as, for example, an antibacterial agent, antiviral agent, bactericide, or viricide, the effect is greater when the particle size is in the 100 nm or less range, which is close to the size of bacteria and viruses. From this perspective, it is preferable that the average particle size of the metal-containing colloidal silica of the present invention be 1 nm or more and 100 nm or less, and particularly 2 nm or more and 80 nm or less.

The metal-containing colloidal silica obtained by the above procedure has a molar ratio of silicon to metal M (Si/M) in the coating layer, which is the combined mixed layer and silica layer, of 10 to 10,000, preferably 20 to 8,000, and particularly preferably 50 to 5,000. If this molar ratio is less than 10, the colloidal silica becomes unstable, which can lead to the settling or gelation of silica particles. If it exceeds 10,000, the properties of the metal content cannot be utilized.

In the present invention, after step (c), a step of concentrating the metal-containing colloidal silica may be carried out. This concentration is carried out by ultrafiltration. While concentration by evaporation of water may also be used, ultrafiltration is more advantageous in terms of energy consumption.

This section explains the ultrafiltration membranes used when concentrating silica by ultrafiltration. Ultrafiltration membranes are used to separate particles ranging in size from 1 nm to several microns, but because they also target dissolved polymeric substances, filtration accuracy in the nanometer range is expressed in terms of molecular weight cutoff. In this invention, ultrafiltration membranes with a molecular weight cutoff of 15,000 or less are suitable. Using membranes in this range allows for the separation of particles 1 nm or larger. More preferably, ultrafiltration membranes with a molecular weight cutoff of 3,000 to 15,000 are used. Membranes with a molecular weight cutoff of less than 3,000 have too much filtration resistance, resulting in uneconomical processing times, while membranes with a molecular weight cutoff of more than 15,000 result in a low level of purification.

Membrane materials include polysulfone, polyacrylonitrile, sintered metal, ceramic, and carbon, and any of these can be used. Polysulfone membranes are easy to use due to their heat resistance and filtration speed. The membrane can be spiral, tubular, or hollow fiber, and any of these can be used, although hollow fiber membranes are compact and easy to use. It is preferable to concentrate the silica in this process so that the silica concentration is 5 to 50% by mass.

The particle size of the metal-containing colloidal silica obtained by the manufacturing method of the present invention can be a typical particle size of around 5 to 300 nm, as long as the silica particles can maintain a colloidal state. However, when used as, for example, an antibacterial agent, antiviral agent, bactericide, or viricide, the effect is greater when the particle size is in the 100 nm or less range, which is close to the size of bacteria and viruses. From this perspective, it is preferable that the average particle size of the metal-containing colloidal silica of the present invention be 1 nm or more and 100 nm or less, and particularly 2 nm or more and 80 nm or less.

The metal-containing colloidal silica obtained by the above procedure has a molar ratio of silicon to metal M (Si/M) of 10 to 20,000, preferably 20 to 10,000, and particularly preferably 30 to 5,000, depending on the size of the colloidal silica core. If this molar ratio is less than 10, the colloidal silica becomes unstable, which can lead to the settling or gelation of the silica particles. If it exceeds 20,000, the properties of the metal content cannot be utilized.

The metal-containing colloidal silica of the present invention obtained by the above-described manufacturing method has antibacterial, antiviral, bactericidal, and virucidal properties, and can be used as an antibacterial, antiviral, bactericidal, or virucidal agent as is. However, depending on the application, it is preferable to further contain a solvent. The solvent is not particularly limited, and examples include water or an organic solvent. Examples of such organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol.

The metal-containing colloidal silica of the present invention has excellent dispersibility in various resins and little tendency to discolor. Therefore, it can be blended with various resins to produce antibacterial, bactericidal, antiviral, or virucidal resin compositions and molded resin products, such as fibers, films, sheets, pipes, panels, containers, building materials, and structural materials. The metal-containing colloidal silica of the present invention can also be blended with paints and other materials to produce antibacterial, bactericidal, antiviral, or virucidal coating films.

Resin molded articles formed from resin compositions containing the metal-containing colloidal silica of the present invention can be of any shape. Examples include fabric products such as woven fabrics, nonwoven fabrics, mesh fabrics, and knitted fabrics; sheet products such as paper and film; and shaped articles such as plates, rods, boxes, and porous bodies. Furthermore, paints containing the metal-containing colloidal silica of the present invention can be of any form. Examples include powder products such as dusting agents and sprays; liquid or paste products such as brush-applied paints, spray paints, and roller-applied paints; adhesives; and sealants. In addition, the metal-containing colloidal silica can be incorporated into deodorants, antiperspirants, soaps, shampoos, moisturizers, cosmetics, toothpastes, mouthwashes, lubricants, creams, lotions, surface cleaners, laundry detergents, and other products to achieve antibacterial, bactericidal, antiviral, or virucidal properties.

Examples of resin molded articles formed from resin compositions containing the metal-containing colloidal silica of the present invention, and articles using paints containing the metal-containing colloidal silica of the present invention, include freshness-preserving films, sanitary products, kitchen and bath products, toiletries, cosmetics, water treatment products, medical equipment, building materials, and fishing nets. Furthermore, paints containing the metal-containing colloidal silica of the present invention can be added to cement mortar or applied to molded cement concrete to produce antibacterial, bactericidal, antiviral, or virucidal cement concrete products. Resin compositions and paints containing the metal-containing colloidal silica of the present invention can also be used in a variety of other products for the purpose of achieving antibacterial, bactericidal, antiviral, or virucidal properties.

The present invention will be described below using examples. However, the scope of the present invention is not limited to these examples. The properties in the examples were measured using the following methods.

(1) Average particle size: 10 g of a sample was taken, diluted hydrochloric acid was added to adjust the pH to ⁴ , heated to solidify, washed with pure water, re-dried, and then dried at 150°C to obtain a powder sample, and the nitrogen adsorption BET specific surface area SA was measured using a NOVA 4200 manufactured by Quantachrome Corp. The average particle size was calculated using the following formula (1) assuming a silica density of 2.2 g/cm3.

Particle diameter D (nm) = 6 x 10 ³ / [density (g/cm ³ ) x SA (m ³ /g)] (1)

(2) Molar Ratio of Silicon to Metal in Coating Layer The amount of silicon in the metal-containing colloidal silica and the core silica particles was measured by back titration using hydrochloric acid and potassium hydroxide solution. The amount of metal in the metal-containing colloidal silica was measured using an ICP-OES 5100 ICP optical emission spectrometer manufactured by Agilent Technologies. The molar ratio of silicon to metal M in the coating layer was calculated from the obtained measurements using the following formula (2):

Si/M=(Si amount in metal-containing colloidal silica−Si amount in core colloidal silica)/metal M amount in metal-containing colloidal silica (2)

(3) Observation of Metals in the Mixed Layer Metals were observed by element mapping images at a magnification of 1,000,000 times using a transmission electron microscope-energy dispersive X-ray spectrometer (TEM-EDX analyzer; Hitachi High-Tech, HD-2700).
(4) Measurement of Metal Included in Metal-Containing Colloidal Silica An X-ray photoelectron spectrometer (XPS analyzer; manufactured by ULVAC-PHI, PHI5000VersaProbe) was used as the X-ray source, and the metal M was confirmed from the peak of the spectrum obtained.

Example 1
(a) Preparation of silver nitrate-containing activated silicic acid aqueous solution 2,200 g of No. 3 sodium silicate ( _SiO2 : 28.8 mass%, _Na2O : 9.7 mass%, _H2O : 61.5 mass%) was added to 13,750 g of deionized water and mixed uniformly to prepare diluted sodium silicate with a silica concentration of 4 mass%. This diluted sodium silicate was passed through a 4-liter column packed with H-type strongly acidic cation exchange resin (Amberlite (registered trademark) IR120B manufactured by Organo Corporation) that had been regenerated with hydrochloric acid in advance, to dealkalize it, and 14,000 mL of activated silicic acid aqueous solution with a silica concentration of 4 mass% and a pH of 3.1 was obtained.
To 3,283 g of the obtained aqueous solution of activated silicic acid, 0.653 g of silver nitrate was added with stirring to prepare an aqueous solution of activated silicic acid containing silver nitrate.
(b) Preparation of Silver-Containing Colloidal Silica 65 g of colloidal silica (Silicadol 30S, manufactured by Nippon Chemical Industry Co., Ltd.) having an average particle size of 9 nm was diluted with 2,500 g of deionized water and then heated to 95°C to obtain aqueous colloidal silica. A 10% by mass aqueous solution of sodium hydroxide was added to this aqueous colloidal silica to adjust the pH to 9.9, and while heating again and maintaining the temperature at 95°C, 9,074 g of the silver nitrate-containing aqueous activated silicic acid solution was added over 3.2 hours to coat the surface of the colloidal silica with a mixed layer, thereby obtaining silver-containing colloidal silica. The temperature was maintained at 95°C during the addition, and 10% by mass sodium hydroxide was simultaneously added to maintain the pH at 9.5 to 10.5.
(c) Preparation of Silica-Coated Silver-Containing Colloidal Silica Next, 8,415 g of the activated silicic acid aqueous solution obtained in step (a) above was added to the obtained silver-containing colloidal silica over a period of 3.6 hours to coat the surface of the silver-containing colloidal silica with a silica layer. The temperature was maintained at 95°C during the addition, and 10% by mass of sodium hydroxide was simultaneously added to maintain the pH at 9.5 to 10.5. After the addition was completed, the mixture was allowed to cool to room temperature, yielding 16,500 g of silica-coated silver-containing colloidal silica.
The obtained silica-coated silver-containing colloidal silica was subjected to pressure filtration by pump circulation using a hollow fiber ultrafiltration membrane (Microza (registered trademark) UF module SIP-1013, manufactured by Asahi Kasei Corporation) with a molecular weight cutoff of 6,000, and concentrated to a silica concentration of 35% by mass, recovering 1,200 g of silica-coated silver-containing colloidal silica. This silica-coated silver-containing colloidal silica had a pH of 10 at 25°C and an average particle size of 21 nm. Furthermore, the results of ICP optical emission spectrometry showed that the molar ratio of silicon to silver (Si/Ag) in the coating layer of the obtained silver-containing colloidal silica was 2,256. Furthermore, when the obtained silver-containing colloidal silica was analyzed by TEM-EDX, the presence of silver in the mixed layer was not confirmed in the element mapping image. On the other hand, when the silver-containing colloidal silica was analyzed by XPS, a spectrum attributable to metallic silver was obtained. These results confirmed that metallic silver was uniformly and finely dispersed as the metal M in the mixed layer. The mixed layer had an average thickness of 4 nm, and the silica layer had an average thickness of 4 nm.

Example 2
(a) Preparation of silver nitrate-containing activated silicic acid aqueous solution 2,200 g of No. 3 sodium silicate ( _SiO2 : 28.8 mass%, _Na2O : 9.7 mass%, _H2O : 61.5 mass%) was added to 13,750 g of deionized water and mixed uniformly to prepare diluted sodium silicate with a silica concentration of 4 mass%. This diluted sodium silicate was passed through a 4-liter column packed with H-type strongly acidic cation exchange resin (Amberlite (registered trademark) IR120B manufactured by Organo Corporation) that had been regenerated with hydrochloric acid in advance, to dealkalize it, and 14,000 mL of activated silicic acid aqueous solution with a silica concentration of 4 mass% and a pH of 3.1 was obtained.
To 5,027 g of the obtained aqueous solution of activated silicic acid, 0.53 g of silver nitrate was added with stirring to prepare an aqueous solution of activated silicic acid containing silver nitrate.
(b) Preparation of Silver-Containing Colloidal Silica 100 g of colloidal silica (Silicadol 30S, manufactured by Nippon Chemical Industry Co., Ltd.) having an average particle size of 9 nm was diluted with 2,500 g of deionized water and then heated to 95°C to obtain aqueous colloidal silica. A 10% by mass aqueous solution of sodium hydroxide was added to this aqueous colloidal silica to adjust the pH to 9.9, and while heating again and maintaining the temperature at 95°C, 5,027 g of the silver nitrate-containing aqueous activated silicic acid solution was added over 4.2 hours to coat the surface of the colloidal silica with a mixed layer, thereby obtaining silver-containing colloidal silica. The temperature was maintained at 95°C during the addition, and 10% by mass sodium hydroxide was simultaneously added to maintain the pH at 9.5 to 10.5.
(c) Preparation of Silica-Coated Silver-Containing Colloidal Silica Next, 5,233 g of the activated silicic acid aqueous solution obtained in step (a) above was added to the obtained silver-containing colloidal silica over a period of 1.9 hours to coat the surface of the silver-containing colloidal silica with a silica layer. The temperature was maintained at 95°C during the addition, and 10% by mass of sodium hydroxide was added simultaneously to maintain the pH at 9.5 to 10.5. After the addition was completed, the mixture was allowed to cool to room temperature, yielding 14,500 g of silica-coated silver-containing colloidal silica.
The obtained silica-coated silver-containing colloidal silica was subjected to pressure filtration by pump circulation using a hollow fiber ultrafiltration membrane (Microza (registered trademark) UF module SIP-1013, manufactured by Asahi Kasei Corporation) with a molecular weight cutoff of 6,000, and concentrated to a silica concentration of 35% by mass, recovering 1,200 g of silica-coated silver-containing colloidal silica. This silica-coated silver-containing colloidal silica had a pH of 9.9 at 25°C and an average particle size of 21 nm. Furthermore, the results of ICP optical emission spectrometry showed that the molar ratio of silicon to silver (Si/Ag) in the coating layer of the obtained silver-containing colloidal silica was 2,615. The mixed layer had an average thickness of 4 nm, and the silica layer had an average thickness of 2 nm.

Example 3
(a) Preparation of Silver Nitrate-Containing Active Silica Aqueous Solution An active silicic acid aqueous solution and a silver nitrate-containing active silicic acid aqueous solution were prepared in the same manner as in Example 2.
(b) Preparation of Silver-Containing Colloidal Silica Silver-containing colloidal silica was prepared in the same manner as in Example 2.
(c) Preparation of Silica-Coated Silver-Containing Colloidal Silica 8,415 g of the activated silicic acid aqueous solution obtained in step (a) above was added to the obtained silver-containing colloidal silica over a period of 3.6 hours to coat the surface of the silver-containing colloidal silica with a silica layer. The temperature was maintained at 95°C during the addition, and 10% by mass of sodium hydroxide was added simultaneously to maintain the pH at 9.5 to 10.5. After the addition was completed, the mixture was allowed to cool to room temperature, yielding 16,500 g of silica-coated silver-containing colloidal silica.
The obtained silica-coated silver-containing colloidal silica was subjected to pressure filtration by pump circulation using a hollow fiber ultrafiltration membrane (Microza (registered trademark) UF module SIP-1013, manufactured by Asahi Kasei Corporation) with a molecular weight cutoff of 6,000, and concentrated to a silica concentration of 35% by mass, recovering 1,200 g of silica-coated silver-containing colloidal silica. This silica-coated silver-containing colloidal silica had a pH of 10 at 25°C and an average particle size of 25 nm. Furthermore, the results of ICP optical emission spectrometry showed that the molar ratio of silicon to silver (Si/Ag) in the coating layer of the obtained silver-containing colloidal silica was 4,503. The mixed layer had an average thickness of 4 nm, and the silica layer had an average thickness of 4 nm.

Example 4
(a) Preparation of copper sulfate-containing activated silicic acid aqueous solution 700 g of No. 3 sodium silicate (SiO ₂ : 28.8% by mass, Na ₂ O: 9.7% by mass, H ₂ O: 61.5% by mass) was added to 4,375 g of deionized water and mixed uniformly to prepare diluted sodium silicate with a silica concentration of 4% by mass. This diluted sodium silicate was passed through a 4-liter column packed with H-type strongly acidic cation exchange resin (Amberlite (registered trademark) IR120B manufactured by Organo Corporation) previously regenerated with hydrochloric acid to dealkalize, obtaining approximately 5,075 mL of activated silicic acid aqueous solution with a silica concentration of 4% by weight and a pH of 3.1. 2.61 g of copper sulfate pentahydrate was added to 2,062 g of the obtained activated silicic acid aqueous solution while stirring to prepare a copper sulfate-containing activated silicic acid aqueous solution.

(b) Preparation of copper-containing colloidal silica 100 g of colloidal silica (Silicadol 30S, manufactured by Nippon Chemical Industry Co., Ltd.) having an average particle size of 9 nm was diluted with 3,000 g of deionized water and then heated to 95°C to obtain aqueous colloidal silica. A 10% by mass aqueous solution of sodium hydroxide was added to this aqueous colloidal silica to adjust the pH to 9.9, and while heating again and maintaining the temperature at 95°C, 2,062 g of the copper sulfate-containing aqueous activated silicic acid solution was added over 2.2 hours to coat the surface of the colloidal silica with a mixed layer, thereby obtaining copper-containing colloidal silica. The temperature was maintained at 95°C during the addition, and 10% by mass sodium hydroxide was simultaneously added to maintain the pH at 9.5 to 10.5.
(c) Preparation of Silica-Coated Copper-Containing Colloidal Silica Next, 3,788 g of the activated silicic acid aqueous solution obtained in step (a) above was added to the obtained copper-containing colloidal silica over 2.0 hours to coat the surface of the copper-containing colloidal silica with a silica layer. The temperature was maintained at 95°C during the addition, and 10% by mass of sodium hydroxide was added simultaneously to maintain the pH at 9.5 to 10.5. After the addition was completed, the mixture was allowed to cool to room temperature, yielding 10,053 g of silica-coated copper-containing colloidal silica.
The obtained silica-coated copper-containing colloidal silica was subjected to pressure filtration by pump circulation using a hollow fiber ultrafiltration membrane (Microza (registered trademark) UF module SIP-1013, manufactured by Asahi Kasei Corporation) with a molecular weight cutoff of 6,000, and concentrated to a silica concentration of 35% by mass, recovering 500 g of silica-coated copper-containing colloidal silica. This silica-coated copper-containing colloidal silica had a pH of 10 at 25°C and an average particle size of 20 nm. Furthermore, the results of ICP optical emission spectrometry showed that the molar ratio of silicon to copper (Si/Cu) in the coating layer of the obtained copper-containing colloidal silica was 338. Furthermore, when the obtained copper-containing colloidal silica was analyzed by TEM-EDX, the presence of copper in the mixed layer was not confirmed in the element mapping image. On the other hand, when the copper-containing colloidal silica was analyzed by XPS, a spectrum derived from copper oxide (CuO) was obtained. These results confirmed that copper oxide (CuO) was uniformly and finely dispersed as the metal M in the mixed layer. The mixed layer had an average thickness of 2 nm, and the silica layer had an average thickness of 2 nm.

Comparative Example 1
The same procedure as in Example 1 was carried out, except that (c) the preparation of silica-coated silver-containing colloidal silica was not carried out, to obtain silver-containing colloidal silica having no silica layer. This silver-containing colloidal silica had a pH of 10 at 25°C and an average particle size of 18 nm. Furthermore, the results of ICP optical emission spectrometry showed that the molar ratio of silicon to silver (Si/Ag) in the mixed layer of the obtained silver-containing colloidal silica was 761. The average thickness of the mixed layer was 4 nm.

Comparative Example 2
The same procedure as in Example 4 was carried out, except that (c) the preparation of silica-coated copper-containing colloidal silica was not carried out, to obtain copper-containing colloidal silica having no silica layer. This copper-containing colloidal silica had a pH of 10 at 25°C and an average particle size of 15 nm. Furthermore, the results of ICP emission spectrometry showed that the molar ratio of silicon to copper (Si/Cu) in the mixed layer of the obtained copper-containing colloidal silica was 151. The average thickness of the mixed layer was 2 nm.

<Storage stability evaluation>
The colloidal silica obtained in each of the Examples and Comparative Examples was placed in a 100 mL plastic bottle and sealed. The sealed plastic bottle was then left to stand at room temperature in a light-shielded thermostatic chamber. After 7 days of standing, the liquid in the plastic bottle was visually observed, and the storage stability was evaluated according to the following criteria.
○: No precipitate ×: Presence of precipitate

<Evaluation of discoloration resistance>
The colloidal silica obtained in each of the Examples and Comparative Examples was diluted with ion-exchanged water to a _SiO2 concentration of 10%, and filter paper was immersed in the resulting sample solution for 5 minutes. The resulting filter paper was air-dried in a darkened environment, and then exposed to sunlight for 24 hours. The filter paper was then visually observed and evaluated for discoloration resistance according to the following criteria.
○: No discoloration ×: Discoloration

<Bactericidal effect test>
Silver-containing silica sols were prepared by adding deionized water to the silver-containing colloidal silica obtained in Examples 1 and 2 and Comparative Example 1 to adjust the silica concentration to 20% by mass, and the bactericidal effect against Escherichia coli and Staphylococcus aureus was tested using the following method.
Escherichia coli (NBRC3972) and Staphylococcus aureus (NBRC12732) were cultured on nutrient agar medium (manufactured by Eiken Chemical Co., Ltd.) at 35°C ± 1°C for 24 hours, and then diluted with purified water to prepare a bacterial solution with a bacterial count of ¹⁰ - ¹⁰ /mL. 0.1 mL of this bacterial solution was mixed with 10 mL of silver-containing silica sol, stirred, and then allowed to stand at 25°C for 5 minutes to obtain a test solution. This test solution was then inoculated at a 10-fold dilution into SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.) and cultured at 35°C ± 1°C for 48 hours. The viable cell count after culture was counted and the results are shown in Table 2.

From the above results, it can be seen that the silver-containing colloidal silica obtained in Examples 1 and 2 and Comparative Example 1 all have excellent bactericidal properties, but the silver-containing colloidal silica obtained in Examples 1 to 3 is less likely to produce precipitates due to aggregation of colloidal particles, and thus has the effect of improving storage stability. Furthermore, it can be seen that the silver-containing colloidal silica obtained in Examples 1 to 3 also has excellent discoloration resistance. It can also be seen that the copper-containing colloidal silica obtained in Example 4 has excellent storage stability and discoloration resistance compared to Comparative Example 2.

Claims (12)

A metal-containing colloidal silica having a mixed layer in which a metal M is dispersed in silica,
the mixed layer is located between the silica particle serving as the core material and the silica layer located on the surface of the metal-containing colloidal silica;
The metal M is at least one selected from Ag and Cu ,
the molar ratio of silicon to metal M (Si/M) in the coating layer including the mixed layer and the silica layer is 10 or more and 10,000 or less;
A metal-containing colloidal silica in which a metal M is uniformly and finely dispersed in a mixed layer.
Idal silica. 2. The metal-containing colloidal silica according to claim 1 , wherein the mixed layer has a thickness of 1 nm or more and 50 nm or less. 3. The metal-containing colloidal silica according to claim 1, wherein the silica layer has a thickness of 0.5 nm or more and 10 nm or less. 4. The metal-containing colloidal silica according to claim 1 , wherein the particle diameter of the silica particles is 0.5 nm or more and 100 nm or less. 5. The metal-containing colloidal silica according to claim 1 , wherein the molar ratio of silicon to metal M (Si/M) in the mixed layer is 5 or more and 5,000 or less. An agent containing the metal-containing colloidal silica according to any one of claims 1 to 5 . A resin composition comprising the metal-containing colloidal silica according to any one of claims 1 to 5 . A paint containing the metal-containing colloidal silica according to any one of claims 1 to 5 . (a) adding a metal salt compound to an aqueous solution of activated silicic acid to prepare an aqueous solution of activated silicic acid containing a metal salt compound;
(b) reacting the metal salt compound-containing aqueous activated silicic acid solution under alkaline conditions in the presence of colloidal silica to form a mixed layer on the surface of the colloidal silica, in which the metal is uniformly and finely dispersed in the silica; and (c) reacting the colloidal silica that has formed the mixed layer with the aqueous activated silicic acid solution under alkaline conditions to form a silica layer on the surface of the mixed layer.
A method for producing metal-containing colloidal silica, comprising:
The method for producing metal-containing colloidal silica, wherein the metal of the metal salt compound is at least one selected from Ag and Cu . 10. The method for producing metal-containing colloidal silica according to claim 9 , wherein the activated aqueous silicic acid solution is obtained by contacting an aqueous silicic acid solution with a cation exchange resin. 11. The method for producing metal-containing colloidal silica according to claim 9 , wherein the metal salt compound is at least one selected from the group consisting of nitrates, chlorides, acetates, phosphates, and sulfates. The method for producing metal-containing colloidal silica according to any one of claims 9 to 11 , further comprising, after the step (c), a step of concentrating the metal-containing colloidal silica.