JP4994611B2 - Composite oxide particles and method for producing the same - Google Patents

Description

  The present invention relates to composite oxide particles coated with an inorganic oxide film and a method for producing the same. More specifically, the present invention relates to composite oxide particles (composite inorganic oxide particles) having a spherical shape and uniform particle size by using oxide particles having a uniform particle size as core particles, and a method for producing the same. It is.

As a conventional method for coating the particle surface with a metal oxide, as described in Patent Document 1, monodispersed silica fine particles (spherical fine particles) are added to an alcohol solvent, which is a polar solvent, and subjected to ultrasonic treatment for dispersion. Then, water adjusted to pH 2 is added and mixed to form a dispersion of silica fine particles, and a methanol solution of Ti (Oi-C ₃ H ₇ ) ₄ is stirred into a dispersion of silica fine particles maintained at 30 ° C. There is a method of mixing while dropping.

  Further, as described in Patent Document 2, a core particle is added to and dispersed in a metal alkoxide dissolved in a polar solvent such as alcohol or ketone, and then water is added to hydrolyze the metal alkoxide so that the metal surface has a metal surface. A method of forming an oxide film is also known.

  On the other hand, as described in Patent Document 3, titanium sulfate, zirconium sulfate or the like, which is a metal salt such as titanium or zirconium, is used as a raw material, and an aqueous solution of these metal salts is slowly dropped into the reaction system to form a metal hydroxide Alternatively, a method of depositing metal oxide around the base particles is also known.

Further, as described in Patent Document 4 and Patent Document 5, as a method of coating a titanium oxide film, a method using a titanium (IV) chloride solution is also known.
JP-A-5-257150 JP-A-6-228604 JP 2000-345072 A JP 2004-123801 A JP 2002-241644 A

  However, in the method of coating an inorganic oxide thin film on the particle surface by reaction with a metal alkoxide in a polar solvent solution, water that hydrolyzes the metal alkoxide is present everywhere in the reaction system, and the core oxidation. There is a problem in that oxide particles present in a single composition are by-produced without covering the surface of the product particles.

  On the other hand, when titanium sulfate, zirconium sulfate or the like, which is a metal salt such as titanium or zirconium, is used as a raw material, although there is a merit of low load on cost and environment that an aqueous solvent can be used, the reaction rate of titanyl sulfate is high. The film formation operation takes time because it is slow, and there is a limit to the thickness of the titanium oxide film that can be coated by one film formation operation. There was a problem that it was necessary to divide into multiple times.

  Further, when a titanium chloride solution is used as a film forming raw material, the solution reaction is severe and dangerous, and there is a problem that chlorine and hydrochloric acid gas is generated. In addition, peroxide is added at the stage of preparing the film-forming solution. However, peroxide may be explosive in some cases, and it is better not to use this reagent for safety. . Although attempts have been made to stabilize by adding carboxylic acid instead of peroxide, it is necessary to add an alkali containing an alkali metal to control the pH value, and for the purpose of forming a high-purity film. Cannot be used.

  Furthermore, all the synthesis methods described above have problems in that it is difficult to control the thickness of the oxide film, and it is impossible to synthesize the desired thickness. Furthermore, there is a problem that the yield of the raw material for forming the film is low.

  The present invention has been made in view of the circumstances as described above. The purpose of the present invention is to <1> suppress by-product formation of single particles of the coating composition, <2> excellent controllability of the thickness of the coating, <3 The object of the present invention is to provide a method for producing composite oxide particles with little loss during the process of the metal alkoxide as a raw material for film formation, that is, high yield of the raw material film, and composite oxide particles obtained thereby.

The inventors of the present application have made extensive studies in order to achieve the above object. As a result, the core oxide particles are dispersed in a nonpolar organic solvent, then water is added, and then the metal alkoxide of the film forming raw material dissolved in the nonpolar organic solvent is added dropwise to achieve the above object. The present inventors have found that this can be done and have completed the present invention.
The composite oxide particles coated with the inorganic oxide film produced by the method according to claim 1 are produced by the following steps (1) to (3) in order to solve the above problems. It is characterized by.

(1) Step of preparing a dispersion by adding inorganic oxide particles as a core to a non-polar organic solvent and dispersing (2) Step of adding water to the dispersion to adsorb water molecules on the surface of the core particles (3) Adding a metal alkoxide dissolved in a polar organic solvent to the dispersion

According to said structure, the controllability of film | membrane thickness is high, the reaction yield of a film formation metal oxide is high, and the byproduct of the single oxide particle of a film | membrane composition can be decreased.

In order to solve the above problem, the method for producing the composite oxide particles according to claim 2 is characterized in that the inorganic oxide particles serving as the core are oxide particles having a uniform particle size obtained by a sol-gel method. And at least one oxide particle selected from the group consisting of silica, titania, zirconia, alumina, and tantalum oxide.

  According to this configuration, since the inorganic oxide particles as the core are produced by the wet method of the diesel method, the particle size distribution is narrower than the particles by the CVD method and other methods, and the residual hydroxyl amount on the particle surface is reduced. Therefore, the surface performance is excellent in preferentially adsorbing water on the surface of the inorganic oxide particles, which is an important point in the present invention.

In order to solve the above problems, the method for producing composite oxide particles according to claim 3 is characterized in that the metal alkoxide dissolved in the nonpolar organic solvent has the following structure.
M _n (OR) _x
(However, M is a metal element capable of forming a metal alkoxide, O is an oxygen atom, R is a linear or branched alkyl group having 1 to 12 carbon atoms, and n and x are integers.)
When this metal alkoxide is used, it becomes easier to dissolve in a non-polar solvent, so it is possible to suppress side reactions that occur outside the surface of the core particle due to high reactivity with water, and the core oxidation It becomes possible to make the reaction on the surface of the object particle dominant. For this reason, control of the film thickness is facilitated, and the reaction yield of the metal alkoxide used for film formation can be increased.

  In order to solve the above problems, the method for producing composite oxide particles according to claim 4 is such that M of the metal alkoxide dissolved in the nonpolar organic solvent is Li, Na, Mg, Ti, Al, Si, P , B, Zr, In, Sn, Zn, V, Nb, W, and Ta, at least any one metal element selected from the group consisting of Ta is included.

  When a metal alkoxide of the above metal element is used as a raw material, it can be easily obtained industrially, the film property of the oxide film is good, and a good film can be formed.

In order to solve the above-mentioned problem, the method for producing composite oxide particles according to claim 5 further includes (4) a step of terminating the reaction of unreacted metal alkoxide as a reaction completion treatment step, The method for producing composite oxide particles according to any one of claims 1 to 4, wherein any one of (4-A) and (4-B) is performed.
(4-A) Step of aging under room temperature, heating, or pressure (4-B) Step of adding a large amount of excess water According to the above configuration, unreacted metal alkoxide is obtained by completing the reaction. By eliminating the by-product of oxide particles having a single composition other than the target oxide-coated particles and adjusting the timing to stop the reaction, the thickness of the film can be controlled.

  In the method for producing the composite oxide particles of the present invention, first, the inorganic oxide particles serving as the core are dispersed in a nonpolar organic solvent, whereby the hydrolysis reaction of the metal alkoxide that forms the film becomes the core having moisture. It can be limited only to the surface of the inorganic oxide particles. In addition, if water is added to the inorganic oxide particles dispersed in the nonpolar organic solvent before the addition of the metal alkoxide, the water collects on the surface of the core particles having many residual hydroxyl groups and is adsorbed on the surface of the core particles, and the water in the reaction system Is limited to the core particle surface. For this reason, the hydrolysis reaction and polycondensation reaction of the metal alkoxide necessary for the formation of the coating proceeds only on the surface of the core particle, and as a result, the by-product of the inorganic oxide particles of the coating component can be suppressed. In addition, the hydrolysis polycondensation reaction of metal alkoxide for film formation has few side reactions and high reaction yield, so the film thickness of the film is controlled by the amount of water used in the reaction and the amount of metal alkoxide. It becomes possible by appropriately deciding. In addition, since the core particles are particles by the diesel method, and there are many residual hydroxyl groups on the surface, the above effect is greater than the particles by other manufacturing methods. Furthermore, the particles by the diesel method have a feature that the particle size distribution is narrower than the other.

  Therefore, it is possible to form an inorganic oxide film of another composition on the surface of monodisperse inorganic oxide particles having a narrow particle size distribution, control the film thickness, and provide a production method with few by-product particles. Play.

One embodiment of the present invention will be described below.
[Inorganic oxide particles as core]
As a synthesis method of the inorganic oxide particles (core particles) serving as the core, the following methods are generally mentioned.
1) A method of converting chlorides such as silicon tetrachloride and titanium tetrachloride into oxide fine particles such as silicon oxide and titanium oxide by a CVD process. According to this method, the particle size is small and spherical, but the fine particle size distribution tends to be wide.
2) A method of preparing a metal oxide by adjusting the pH value of an aqueous solution of a metal salt such as aluminum nitrate from acidic to basic and salting out. According to this method, the particle shape is indefinite, the particle size is large, and the particle size distribution tends to be wide.

Since it is possible to form a metal oxide on the surface of inorganic oxide particles prepared by the general method as described above by the production method of the present invention, it is not necessarily excluded from the core particles targeted by the present invention. It is not something.
3) On the other hand, a method of using metal alkoxide as a raw material to produce metal oxide particles under basicity to form inorganic oxide particles is well known as a sol-gel method.

The sol-gel method is characterized by high controllability of particle size, and easily obtains spherical particles with a narrow particle size distribution, and is optimal as the core particle according to the present invention. However, the core particles that can be produced by this method are not particularly limited in composition, but silica, titania, zirconia, alumina, and tantalum oxide, which are generally easy to synthesize, are suitable.
The particle diameter of the core particles obtained as described above is not particularly limited, and those in the range of nanometer size to micron order size are more preferably used.

  The method for coating the surface of the core particle of the present invention with a metal oxide is as follows.

  The aforementioned core particles are dispersed in a nonpolar solvent. As the nonpolar solvent, an aliphatic solvent such as hexane which is generally easily available, an alicyclic solvent such as cyclohexane, an aromatic solvent such as toluene and xylene, and the like are preferable. In addition, an epoxy monomer or a vinyl monomer such as styrene or methacrylic acid ester can be selected as the nonpolar solvent depending on the case.

  As a method of dispersing the core particles in the nonpolar solvent, not only stirring using a stirring blade and a stirring bar, but also the use of ultrasonic vibration, a homomixer, a ball mill or a planetary mill is effective for increasing the degree of dispersion. .

Subsequently, water is added to the core particle dispersion, and the mixture is allowed to stand for about 1 minute to 1 hour until the water collects on the surface of the core particles. It is effective to shorten the time to perform a process such as stirring during this period. The water to be added is usually neutral, but it needs to be acidic or basic when coated with silica. Therefore, the pH value of the added water is not particularly limited.
Usually, the amount of water added is preferably 2 to 100 times the amount of metal alkoxide. However, since the thickness of the metal oxide film to be coated varies depending on the amount of water added, it is necessary to experimentally determine the relationship between the metal alkoxide and the amount of water added to the desired film thickness in advance.

Subsequently, as the metal alkoxide for forming a film, the following are available because they are commercially available. Of course, the present invention is not limited to the following metal alkoxides, and other types of metals or different kinds of alkoxide alcohols can be used.
Li-related alkoxides: Li (OCH3), Li (OC2H5), Li (OC3H7), Li (OC4H9)
Na-related alkoxides: Na (OCH3), Na (OC2H5), Na (OC3H7), Na (OC4H9)
Mg-related alkoxides: Mg (OCH3) 2, Mg (OC2H5) 2, Mg (OC3H7) 2, Mg (OC4H9) 2
Ti-related alkoxides: Ti (OCH3) 4, Ti (OC2H5) 4, Ti (OC3H7) 4, Ti (OC4H9) 4
Al-related alkoxides: Al (OCH3) 3, Al (OC2H5) 3, Al (OC3H7) 3, Al (OC4H9) 3
Si-related alkoxides: Si (OCH3) 4, Si (OC2H5) 4, Si (OC3H7) 4, Si (OC4H9) 4
P-related alkoxides: P (OCH3) 3, P (OC2H5) 3, P (OC3H7) 3, P (OC4H9) 3, P (OCH3) 5, P (OC2H5) 5, P (OC3H7) 5, P (OC4H9 )Five
B-related alkoxides: B (OCH3) 3, B (OC2H5) 3, B (OC3H7) 3, B (OC4H9) 3
Zr-related alkoxides: Zr (OCH3) 4, Zr (OC2H5) 4, Zr (OC3H7) 4, Zr (OC4H9) 4
In-related alkoxides: In (OCH3) 3, In (OC2H5) 3, In (OC3H7) 3, In (OC4H9) 3
Sn-related alkoxides: Sn (OCH3) 4, Sn (OC2H5) 4, Sn (OC3H7) 4, Sn (OC4H9) 4
Zn-related alkoxides: Zn (OCH3) 2, Zn (OC2H5) 2, Zn (OC3H7) 2, Zn (OC4H9) 2
V-related alkoxides: VO (OCH3) 3, VO (OC2H5) 3, VO (OC3H7) 3, VO (OC4H9) 3, V (OCH3) 5, V (OC2H5) 5, V (OC3H7) 5, V (OC4H9 )Five
Nb-related alkoxides: NbO (OCH3) 3, NbO (OC2H5) 3, NbO (OC3H7) 3, NbO (OC4H9) 3, Nb (OCH3) 5, Nb (OC2H5) 5, Nb (OC3H7) 5, Nb (OC4H9 )Five
W-related alkoxides: W (OCH3) 5, W (OC2H5) 5, W (OC3H7) 5, W (OC4H9) 5
Ta-related alkoxides: Ta (OCH3) 5, Ta (OC2H5) 5, Ta (OC3H7) 5, Ta (OC4H9) 5
In addition, since many of these metal alkoxides are highly reactive, carboxylic acids such as acetic acid, formic acid and oxalic acid, and β-diketones such as acetylacetonato are used to control the reactivity. 1 to 10 times mol may be added.
Since the above metal alkoxide is soluble in a nonpolar solvent, it is used as a nonpolar solution for the film formation reaction on the core particles.

A metal alkoxide solution is added dropwise to the non-polar solution of core particles to which water has been added.
Since the metal alkoxide undergoes a hydrolysis reaction as soon as it comes into contact with water, and subsequently causes a polycondensation reaction, in most cases, either a metal alkoxide or water in the reaction system is left to stand for several hours to 10 hours. Is consumed and the reaction ends.

  In most cases, the film formation reaction is completed at room temperature, but if the metal alkoxide is a slightly slow hydrolysis reaction such as Si, Ta, V, W, B, The reaction can be completed efficiently by raising the reaction temperature from 50 ° C to about 100 ° C. Alternatively, it is also effective to add water for the completion of the reaction.

  The particles having a film formed by the above reaction can be collected by a method such as filtration or centrifugation. The recovered composite particles may be heat-treated as necessary. For example, when a film is formed with titania, it is effective to heat the film layer to a temperature higher than its crystallization temperature when it is necessary to make the film layer into crystals such as anatase or rutile.

  The thickness of the inorganic oxide film according to the present invention is not particularly limited, and a nanometer size range is particularly preferably used.

  Applications of the composite particles of the present invention include, for example, conductive fillers, ultraviolet cut films, infrared cut films, proton conductors used in fuel cells, and the like.

[Example 1]
Silica particles were prepared by the following sol-gel method.
300 g of water was added to 60 g of commercially available 28% aqueous ammonia, and 300 ml of ethanol was added to prepare an ammonia solution, which was designated as solution A. Subsequently, 67 g of tetraethoxysilane was dissolved in 300 ml of ethanol to obtain a solution B. Liquid B was slowly added dropwise to liquid A at room temperature. After standing overnight, the particles were collected by centrifugation and vacuum dried at 50 ° C. for 24 hours. Silica particles having a uniform particle diameter of 350 nm were obtained. The SEM image is shown in FIG.

  By the way, the particle size of the silica particles can be controlled by changing the amount of 28% ammonia water used in the liquid A. When the amount of 28% ammonia water used is 12 g, the particle size becomes 50 nm and 28% When the amount of ammonia water used is 20 g, the particle size becomes 100 nm, and when the amount of 28% ammonia water used is 30 g, the particle size becomes 170 nm and the amount of 28% ammonia water used is 120 g. In this case, the particle size was 500 nm. Accordingly, silica particles having a desired particle diameter can be obtained, and the silica particles thus obtained were used in the following examples.

60 g of the silica particles having a particle diameter of 370 nm obtained above were dispersed in 2400 ml of toluene. In order to increase the degree of dispersion, dispersion treatment was performed with an ultrasonic vibrator. 18 g of water was added to this solution and stirred well to adsorb water onto the surface of the silica particles. This is a water adsorption dispersion. Subsequently, 284 g of titanium tetraisopropoxide (Ti (Oi-C3H7) 4) was dissolved in 1650 ml of toluene to obtain an alkoxide solution. This alkoxide solution was added to the water adsorption dispersion and stirred for 48 hours. This reaction solution was centrifuged, and after removing the supernatant, fresh toluene was added, and the supernatant was removed again by centrifugation, followed by washing. This washing operation was repeated three times.
Through the above operation, silica particles coated with titania were obtained. The titania-coated silica particles are shown in FIG. As can be seen from this SEM photograph, the surface of the particles was uniformly coated with titania, and no feared by-product of titania single particles was observed. When the diameter of the titania-coated silica particles was measured from this SEM image, it was 385 nm. Therefore, the thickness of the titania coating could be estimated to be about 7 nm.

[Example 2]
In the titania coating reaction performed in Example 1, the amount of water added to adsorb on the silica particles was simply doubled and doubled that of Example 1, and the other treatments were reacted in exactly the same manner. However, as shown in FIG. 3, the recovered titania-coated silica particles were able to increase the thickness of the titania coating. When the amount of water added was twice, the titania coating thickness could be estimated to be about 15 nm. Further, when the amount of water added was 5 times, the titania coating thickness could be estimated to be about 25 nm.
From the above, it was found that the titania coating thickness can be controlled by the amount of water added.

Example 3
In the coating reaction performed in Example 1, the silica particles used had a particle diameter of 350 nm, and the type of metal oxide to be coated was aluminum, so that the type of metal oxide used was aluminum triisopropoxy. (Al (Oi-C3H7) 3), and all other conditions such as the amount added were the same. As shown in FIG. 4, the alumina-coated silica particles recovered from the alumina coating reaction were uniformly coated with alumina on the particle surface. Moreover, the byproduct of the alumina single particle which was afraid was not seen. When the diameter of the alumina-coated silica particles was measured from this SEM image, it was 365 nm. Therefore, the thickness of the alumina coating could be estimated to be about 7 nm.

Example 4
In the alumina coating reaction performed in Example 3, silica particles having a particle size of 300 nm were used, and the amount of water added for adsorption was doubled and five times that of Example 3 , and aluminum triisopropoxide was further added. The amount used was 2 times and 5 times that of Example 3 and the other treatments were reacted in exactly the same manner. As shown in FIG. 5, the recovered alumina-coated silica particles were thickened as shown in FIG. did it. When the amount of water added was double (at this time, aluminum triisopropoxide was doubled), the alumina coating thickness could be estimated to be about 10 nm. Furthermore, when the amount of water added was 5 times (at this time, aluminum triisopropoxide was also 5 times), the alumina coating thickness could be estimated to be about 15 nm.
From the above, it was found that the alumina coating thickness can be set to a desired thickness by controlling the amount of water and the amount of metal alkoxide added.
In this case, however, it can be seen that when the amount of water added is twice or more, single particles of alumina are by-produced.

Example 5
In the coating reaction performed in Example 1, silica particles having a particle size of 320 nm were used, and the type of metal oxide to be coated was phosphorous oxide. Therefore, the type of metal oxide used was phosphorous oxytriethoxide ( PO (OC2H5) 3) and all other conditions such as the amount added were the same. The phosphorus-coated silica particles recovered from the phosphorus-coating reaction were uniformly coated with phosphorus oxide as shown in FIG. However, in this case, a part of the phosphorus oxide coating layer was removed during the cleaning of the recovered phosphorus-coated particles, and the coating thickness was very thin. However, in this case as well, the by-product of the feared phosphorus oxide single particles was not seen, and a coating layer could be formed uniformly. When the diameter of the phosphorus oxide-coated silica particles was measured from this SEM image, the coating thickness could not be measured because it was hardly different from the core silica particles.

Example 6
In the coating reaction carried out in Example 1, silica particles having a particle size of 320 nm were used, and the type of metal oxide to be applied was lithium oxide, so that the type of metal oxide used was lithium ethoxide (Li (OC2H5 )), And all other conditions such as the amount added were the same. Also in this case, the surface of the particles was uniformly coated with lithium oxide. However, in this case, a part of the lithium oxide coating layer was removed during the cleaning of the recovered coated particles, and the coating thickness was very thin. However, in this case as well, the by-product of the lithium oxide single particles that had been afraid was not seen, and a coating layer could be formed uniformly. When the diameter of the lithium oxide-coated silica particles was measured from this SEM image, the coating thickness could not be measured because it was almost the same as the core silica particles.

  From the above examples, it was found that the surface of the silica particles can be coated with a uniform metal oxide. It was also found that the coating thickness can be controlled by the amount ratio of water and metal alkoxide to be added. It was also found that the amount of by-product particles having a single composition of the metal oxide in the coating layer was very small. These features are major features of the present invention, and are effects that cannot be obtained by conventional methods.

    The metal oxide-coated oxide particles of the present invention enhance the function of conventional oxide particles having a single composition and can be developed in various application fields. For example, when a metal oxide having a high refractive index and a metal oxide having a low refractive index are coated, composite particles having a controlled refractive index can be obtained, and application to an optical film of a display can be considered. Similarly, when particles having a large dielectric constant and those having a small dielectric constant are combined, composite particles having a desired dielectric constant can be obtained, and application to a semiconductor dielectric insulating film can be considered. Furthermore, when the coating layer is coated with an oxide having high acidity, it can be applied to a proton conductor, and when it is coated with lithium oxide, it can be applied to a lithium ion conductor.

It is a SEM image of the silica particle which concerns on one embodiment of this invention. It is a SEM image of the silica particle before and behind coating with titania. It is a SEM image which shows the influence on the titania coating thickness of the molar ratio of a titanium alkoxide and addition water. It is a SEM image of the silica particle before and behind coating with alumina. It is a SEM image which shows the influence on the film thickness of Al / Si ratio. Is an SEM image of silica particles before and after coated with P ₂ O _5.

Claims (5)

A method for producing composite oxide particles coated with an inorganic oxide film, which is produced by the following steps (1) to (3).
(1) Step of preparing a dispersion by adding inorganic oxide particles as a core to a non-polar organic solvent and dispersing (2) Step of adding water to the dispersion to adsorb water molecules on the surface of the core particles (3) Adding a metal alkoxide dissolved in a polar organic solvent to the dispersion   The core inorganic oxide particles are oxide particles having a uniform particle diameter obtained by a sol-gel method, and at least one oxidation selected from the group consisting of silica, titania, zirconia, alumina, and tantalum oxide. The method for producing composite oxide particles according to claim 1, wherein the composite oxide particles are product particles. The method for producing composite oxide particles according to claim 1 or 2, wherein the metal alkoxide dissolved in the nonpolar organic solvent has the following structure.
M _n (OR) _x
(However, M is a metal element capable of forming a metal alkoxide, O is an oxygen atom, R is a linear or branched alkyl group having 1 to 12 carbon atoms, and n and x are integers.)   M includes at least one metal element selected from the group consisting of Li, Na, Mg, Ti, Al, Si, P, B, Zr, In, Sn, Zn, V, Nb, W, and Ta The method for producing composite oxide particles according to claim 3. The reaction completion treatment step further includes (4) a step of terminating the reaction of the unreacted metal alkoxide, and at least one of the following treatments (4-A) and (4-B) is performed: The method for producing a composite oxide particle according to any one of 1 to 4.
(4-A) Step of aging under room temperature, heating, or pressure (4-B) Step of adding a large amount of excess water