JP4644390B2 - Method for producing silica-coated metal composite powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a silica-coated metal-based composite powder and a silica-coated metal-based composite powder obtained by the method. More specifically, the present invention is a metal-based composite powder that is substantially free of agglomerated particles and silica particles, has a uniform and dense silica coating on the surface, and is useful for various applications as a functional powder. The present invention relates to a method for efficiently producing the silica-coated metal-based composite powder obtained by this method.
[0002]
[Prior art]
Conventionally, metal powders, alloy powders, intermetallic compound powders and metal compound powders have various applications in various fields depending on their chemical, mechanical, electrical, thermal and optical properties. Various surface modifications have been carried out in order to effectively exhibit the function according to each application or to exhibit two or more combined functions. . Known surface modification methods for powders include, for example, coating modification, topochemical modification, mechanochemical reaction modification, encapsulation modification, high energy utilization modification, and precipitation reaction modification. ing.
[0003]
Specifically, a magnetic powder is used for the magnetic toner, and the color tone of the magnetic powder is not a problem with the conventional black magnetic toner, but the color tone cannot be used with the color magnetic toner. In this case, it is necessary to perform a surface modification treatment of the magnetic powder to change the color tone of the surface to one that can be used for the color magnetic toner. In addition, a heat dissipation material used as a filling material for a semiconductor sealing material cannot be used only with a metal powder having good thermal conductivity, and must be electrically insulating. It must have a film with sufficient electrical insulation on the surface. Therefore, it is necessary to perform a surface modification treatment of the metal powder and provide an insulating coating on the particle surface.
[0004]
Therefore, in order to cope with such a situation, for example, a metal oxide or metal compound powder is dispersed in a metal alkoxide solution, and the metal alkoxide is hydrolyzed to form a metal oxide on the surface of the metal or metal compound powder. Has been disclosed to form a film of the metal oxide (JP-A-6-228604). However, in this method, when surface treatment is performed on metal or metal compound powder of micron size or more, due to the specific gravity of the powder and poor adaptability to the reaction solvent, in the reaction solvent, uniformly as individual particles. It is extremely difficult to disperse, and when the reaction is carried out in this state, it is a matter of course that the surface is coated in an agglomerated state, causing a problem that a homogeneous and dense film is not formed.
[0005]
On the other hand, rare earth magnets with high magnetic properties are now indispensable for miniaturization of electronic products such as communication equipment and information processing equipment that can make magnets smaller and smaller. Yes. In particular, rare earth bonded magnets have an excellent shape processability and can be formed into thin and minute shapes, so that the amount of use thereof continues to increase.
[0006]
By the way, in recent years, a photocatalyst represented by titanium dioxide is expected as an environmental catalyst, and has begun to be applied to the decomposition of many harmful organic substances such as NOx, dioxin, and indoor VOC (volatile organic chemicals). However, this photocatalyst has a strong oxidizing power that is a photocatalytic action, so it is necessary to devise measures such as selecting an inorganic substance for the binder or preventing the photocatalyst and the resin from coming into direct contact with each other. It was one. For this reason, it has been attempted to coat the surface of titanium dioxide fine particles as a photocatalyst with a silica-based porous material having fine voids. Such photocatalyst is not directly touched by titanium dioxide even when it comes into contact with organic substances such as resin, so that deterioration of the organic substance is suppressed, and it is used by mixing with paint, resin, paper, fiber, etc. Is possible.
[0007]
[Problems to be solved by the invention]
Under such circumstances, the present invention is a metal-based composite powder that is substantially free of agglomerated particles and silica particles, has a uniform silica coating on the surface, and is useful as a functional powder for various applications. It aims at providing the method of manufacturing a body efficiently.
[0008]
[Means for Solving the Problems]
As a result of intensive research to achieve the above-mentioned object, the present inventors have dispersed metal-based powder in a colloidal silica slurry having silanol groups on the surface, and irreversible aggregation between colloidal silicas having silanol groups. Drying is performed under conditions that do not generate water, and then the obtained dry powder is redispersed in a solvent in which colloidal silica can be dispersed, and excess colloidal silica that does not contribute to coating is removed by wet classification. Thus, it has been found that the object can be achieved, and the present invention has been completed based on this finding.
[0009]
That is, the present invention
(1) Metal-based powder comprising colloidal silica having a silanol group on the surface and an average particle size of 0.5 to 500 μm and comprising at least one powder selected from metals, alloys, intermetallic compounds and metal compounds The slurry containing the body is freeze-dried, and then the obtained dry powder is redispersed in a solvent in which colloidal silica can be dispersed to classify and remove excess colloidal silica that does not contribute to coating. A method for producing a silica-coated metal-based composite powder characterized by
(2) The method according to (1), wherein the slurry is adjusted to have a viscosity of 0.15 Pa · s or more, and the drying treatment is performed in a state where the dispersion state is maintained.
(3) The method according to (1) or (2), wherein in the freezing step in lyophilization, the slurry is cooled and frozen with stirring.
(4) The method according to any one of (1) to (3), wherein the obtained silica-coated metal-based composite powder is further subjected to a heat treatment at 50 to 1200 ° C.
[0010]
(5) The method according to any one of (1) to (4), wherein the average particle size of the colloidal silica is 1/10 or less of the average particle size of the metal-based powder and 1 to 200 nm.
(6) The method according to any one of (1) to (5), wherein the content ratio of the colloidal silica and the metal-based powder in the slurry is a weight ratio of 3:97 to 50:50.
( 7 ) The method according to any one of (1) to ( 6 ), wherein the slurry containing colloidal silica and metal powder is an aqueous slurry, and ( 8 ) the metal powder is nickel (1 ) To ( 7 ) any one of the methods,
Is to provide.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the metal-based powder used as the core particle is a metal powder, an alloy powder, an intermetallic compound powder, and a metal compound powder. Things can be mentioned. Specifically, iron, nickel, chromium, cobalt, titanium, zirconium, tin, copper, aluminum, zinc, etc., and alloys, oxides, composite oxides, Sm—Co alloys, Nd—Fe—B alloys, etc. Alloys, Sm—Fe—N alloys, Ce—Co alloys, magnetic materials such as Sr ferrite and Ba ferrite, tin doped indium oxide (ITO), antimony doped tin oxide (ATO), tungsten oxide, barium titanate Among the powders such as (BaTi ₄ O ₉ ), strontium titanate (SrTiO ₃ ), sodium titanate (Na ₂ Ti ₆ O ₁₃ ), cadmium sulfide, etc. Depending on the type, one or more types are appropriately selected and used.
[0012]
The average particle size of the metal-based powder is selected in the range of 0.5 to 500 μm. When the average particle size is in the above range, the particle size of the metal-based powder can be made 10 times or more than colloidal silica, and the particle surface of the metal-based powder is sufficiently covered with silica. It becomes possible. A more preferable average particle size of the metal-based powder is 1 to 100 μm, and more preferably 1 to 50 μm.
[0013]
In the method of the present invention, first, the metal powder is dispersed in a colloidal silica slurry having silanol groups on the surface to obtain a slurry of colloidal silica and metal powder. Here, colloidal silica is not particularly limited as to its production method, and those produced by a conventionally known method can be used. For example, hydrolyzed / condensed aqueous solution containing sodium metasilicate, sodium orthosilicate or water glass with mineral acid or acidic ion exchange resin, and tetraalkoxysilane in aqueous medium However, when the obtained silica-coated metal-based composite powder is used as a filler for electronic materials that dislike ionic impurities such as alkali metal ions, a tetraalkoxy is used. A method obtained by hydrolysis / condensation of silane, that is, a so-called sol-gel method is preferred.
[0014]
There is no restriction | limiting in particular as a solvent used for this colloidal silica slurry, For example, organic solvent type | system | group solvents, such as an aqueous solvent and alcohol, can be used, However, Considering environment, operativity, etc., an aqueous solvent is preferable. In addition, it is advantageous to use the colloidal silica slurry thus obtained as it is without drying. When the colloidal silica slurry is subjected to a drying treatment, agglomeration occurs particularly in the drying treatment. When the dried colloidal silica is redispersed in an aqueous solvent to prepare a slurry, the aggregate of colloidal silica is formed on the surface of the metal powder particles. Is coated, and it is difficult to form a flat silica film.
[0015]
If the average particle size of the colloidal silica in the colloidal silica slurry used in the present invention is too small, the cohesive force is too strong and aggregates via the colloidal silica are generated. On the other hand, if it is too large, the cohesive force and adhesive force become weak, and the adhesiveness with the metal powder decreases. Therefore, it is preferably 1/10 or less and 1 to 200 nm with respect to the metallic powder, more preferably 10 to 150 nm, and particularly preferably 30 to 120 nm. Further, the amount of the metal-based powder dispersed in the colloidal silica slurry varies depending on the surface area of the metal-based powder in order to uniformly provide a uniform and dense silica coating on the particle surface of the powder. The weight ratio of the colloidal silica to the metal-based powder is usually selected to be in the range of 3:97 to 50:50, preferably 5:95 to 40:60, more preferably 5:90 to 30:70. It is good. Although it is necessary to add a sufficient amount of colloidal silica to the surface area of the metal-based powder, it is not economical to add too much.
[0016]
The metal-based powder can be dispersed in the colloidal silica slurry by mechanical stirring and / or ultrasonic irradiation. In this invention, what concentrated the slurry containing the colloidal silica and metal type powder which were obtained in this way in a homogeneous dispersion state can also be used. The concentration is preferably performed by heating under reduced pressure.
[0017]
Next, the slurry in which the colloidal silica and metal powder thus obtained are uniformly dispersed is dried under conditions that do not cause irreversible aggregation between the colloidal silica. When the heating temperature during the drying process is high, the aggregation between the colloidal silicas becomes strong, and as a result, it becomes difficult to prevent the aggregation of the silica-coated metal-based composite powder. Therefore, the drying treatment is preferably performed at a temperature of 40 ° C. or lower, and vacuum drying, spray drying, freeze drying, and the like can be applied as the method, and freeze drying is particularly preferable.
[0018]
As a pretreatment for this drying treatment, the slurry containing colloidal silica and metal powder in a homogeneous dispersion state is concentrated and adjusted so that the viscosity is 0.15 Pa · s or more, and the dispersion state is maintained. By performing the drying treatment, a silica film can be formed without unevenness on the surface of the metal-based powder. When the viscosity is less than 0.15 Pa · s, the metal-based powder and colloidal silica cause phase separation due to the difference in particle diameter and specific gravity, and a surface-free silica coating is not formed on the particle surface of the powder. The object of the present invention cannot be achieved. A preferable viscosity is 0.5 to 4.0 Pa · s, and a range of 0.8 to 3.0 Pa · s is particularly preferable. The concentration is preferably carried out by simultaneously performing a stirring operation using an evaporator or the like and heating under reduced pressure.
[0019]
On the other hand, a silica film can be formed on the surface of the metal-based powder without any spots by stirring and drying the slurry containing colloidal silica and the metal-based powder while maintaining a homogeneous dispersion state. In particular, before the freeze-drying treatment, the stirring operation such as rotating the container containing the slurry is performed, and the slurry is cooled and frozen while keeping the dispersed state of the slurry, and the freeze-drying treatment is performed. Is optimal.
[0020]
Since the metallosiloxane bond (M-O-Si) is formed at the interface between the silica and the metal powder of the silica-coated metal powder obtained by the above method, it is strong due to its chemical bond strength. It is presumed to have good adhesion.
[0021]
The dry powder obtained in this way is preliminarily coated with the metal powder surface without any spots, so that an excessive amount of colloidal silica is charged to the metal powder surface. In addition to the coated metal composite particles, there is a silica component derived from colloidal silica. Therefore, when this dry powder is used as it is as a filler, there is a risk of mixing with the resin, in particular, an increase in viscosity. In the case of molding, spots or the like may occur on the molded body. Therefore, in the present invention, it is desirable to redisperse in a solvent in which colloidal silica can be dispersed, and to perform the operation of removing the silica component by the classification operation utilizing the difference in the sedimentation rate of the particles. Thereby, a metal-based composite powder having a uniform and dense silica coating on the particle surface is obtained. In addition, during the redispersion, mechanical stirring and / or ultrasonic irradiation is performed, but the silica component on the surface of the target silica-coated metal-based composite particles does not fall off, which also indicates the interfacial adhesion. It turns out that it is in a good covering state.
[0022]
In the present invention, the silica-coated metal-based composite powder thus obtained can be subjected to a heat treatment as desired to further improve the strength of the coating. Heat processing temperature is 50-1200 degreeC normally, Preferably, it is 50-800 degreeC, More preferably, it is 100-800 degreeC. In addition to this, it is necessary to set the heat treatment temperature to a temperature at which the functional change of the metal that is the powder to be coated does not occur.
[0023]
Then, treatment with a physical shearing force or impact force using an apparatus such as hybridization or mechanofusion can be performed to further improve the strength of the coating or to make it spherical.
[0024]
In the present invention, as a raw material for the silica coating provided on the surface of the micron-sized metal-based powder, nanometer-sized colloidal silica containing a silanol group on the particle surface is used in a slurry state, so that the cohesive force and dehydration due to the silanol group Condensation can be used to provide a uniform silica coating.
[0025]
When using a silica slurry by a gas phase method instead of the colloidal silica slurry, the silica by the gas phase method has an agglomerated structure, so that a homogeneous and dense silica coating is formed on the particle surface of the metal-based powder. It is difficult to form. Furthermore, since it does not have a silanol group, bonding between the silica coating and the metallic particles or between the silica in the silica coating cannot be expected, so it has excellent adhesion to the metallic particles and is dense and has good strength. It is difficult to form a silica film.
[0026]
Moreover, when a silica coating is provided on the surface of a metal powder particle by hydrolytic condensation using tetraethoxysilane or the like, it is necessary to perform treatment while maintaining a dispersed state without aggregation when attempting to encapsulate completely. Yes, it is necessary to react uniformly in the system and on all particle surfaces. However, especially in the case of micron-sized metal-based powders, they are difficult, so it is difficult to form a uniform silica film on the particle surface without causing aggregation between the particles. Requires very precise control of the condition.
[0027]
In the present invention, when forming a porous silica film having fine voids on the particle surface of the metal powder, for example, it is soluble in a slurry containing colloidal silica and metal powder in an appropriate organic solvent. Organic fine particles or organic fine particles that can be removed by firing are added and the same operation as described above is performed to obtain a silica-coated metal-based composite powder, followed by an organic solvent treatment or a firing treatment. By subjecting the titanium dioxide powder to such an operation, a photocatalyst comprising a titanium dioxide powder having a porous silica coating on the particle surface can be obtained.
[0028]
In the present invention, when the silica-coated metal composite powder obtained as described above is mixed with a resin or the like, the silica-coated metal is optionally used for the purpose of improving wettability with the resin. Surface treatment with a coupling agent can be applied to the composite powder. Examples of the coupling agent include known silane coupling agents, titanate coupling agents, aluminum coupling agents, and the like.
The present invention also provides a silica-coated metal-based composite powder obtained by the above-described method.
[0029]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0030]
Example 1
<Synthesis>
Water containing colloidal silica particles [“High Presica UF” manufactured by Ube-Nitto Kasei Co., Ltd., synthetic raw silica] obtained by hydrolysis and polycondensation reaction of tetraethoxysilane in a 1000 ml eggplant flask 457 g of dispersed silica slurry (silica concentration: 9.85% by weight) was charged, and 255 g of nickel powder having an average particle size of 10 μm was added thereto. Then, it connected to the evaporator and disperse | distributed by stirring and ultrasonic irradiation by rotating for about 1 hour. Subsequently, concentration was performed under reduced pressure at a pressure of 3450 Pa and a temperature of 50 ° C. to remove water and ammonia, and the concentration was continued until the viscosity became high and phase separation between nickel and silica did not occur. The liquid viscosity after the concentration was measured with a vibration viscometer (Viscomate Model VM1G, manufactured by Yamaichi Electronics Co., Ltd.), and as a result, it was 1.6 Pa · s under 20 ° C. conditions.
[0031]
Next, the eggplant flask was allowed to stand in a solution in which dry ice was added to methanol to freeze the slurry, followed by drying with a freeze dryer to obtain a powder. Next, a part of this is added to a glass container, re-dispersed by stirring and ultrasonic irradiation in ion-exchanged water, and allowed to stand. After the target silica-coated nickel powder settles, the cloudy colloidal silica alone floats. The supernatant was removed. Then, the target silica-coated nickel powder was obtained by removing the silica single particles by the classification operation using the difference in the sedimentation rate of adding ion exchange water and redispersing again.
[0032]
<Evaluation>
FIG. 1 shows a scanning electron microscope (SEM) photograph of nickel powder. When this silica-coated nickel powder was observed with a scanning electron microscope (SEM), as shown in FIG. 2, it was confirmed that a silica coating was uniformly formed on the particle surface and that there were substantially no agglomerated particles. .
As a result of measuring the BET specific surface area (Flowsorb II2300, manufactured by Shimadzu Corporation), the Ni powder was 0.425 m ² / g, whereas the silica-coated nickel powder was 4.265 m ² / g. .
Furthermore, as a result of fluorescent X-ray measurement (PW2400 type fully automatic X-ray fluorescence analyzer, manufactured by PHILIPS), Ni was 91 wt% and Si was 3.1 wt%.
[0033]
Example 2
<Heat treatment>
The silica-coated nickel powder obtained in Example 1 was heat-treated in air at 300 ° C. for 12 hours.
[0034]
<Evaluation>
As a result of SEM observation of the silica-coated nickel powder after this heat treatment, it was confirmed that there was substantially no significant change in the particle surface and the aggregated state.
As a result of measuring the BET specific surface area in the same manner as in Example 1, it was 2.025 m ² / g, and it was inferred that the silica coating layer was densified.
[0035]
Example 3
<Mechanical processing>
In Example 1, the powder obtained after lyophilization was treated with a hybridization system (manufactured by Nara Machinery Co., Ltd.) under the condition of 15000 rpm for 30 minutes. Subsequently, it disperse | distributed in ion-exchange water and the classification operation was performed like Example 1. FIG.
[0036]
<Evaluation>
As a result of SEM observation of the silica-coated nickel powder after the hybridization treatment, as shown in FIG. 3, the particles were spheroidized by physical impact, and the silica coating layer was not dropped or aggregated by the treatment. Not confirmed.
[0037]
Example 4
<Synthesis>
The colloidal silica in Example 1 is made into a commercially available Snowtec ZL (silica component concentration 40 wt%, manufactured by Nissan Chemical Co., Ltd.), the charged amount is 113 g, the vacuum concentration step is not performed, and the eggplant flask is rotated and stirred. Thereafter, the same operation was performed except that freeze-drying was performed after freezing.
[0038]
<Evaluation>
When this silica-coated nickel powder was observed with a scanning electron microscope (SEM), as shown in FIG. 4, it was confirmed that a silica coating was uniformly formed on the particle surface and that there were substantially no agglomerated particles. .
[0039]
Example 5
In Example 1, the same operation was performed except that the eggplant flask was rotated after the concentration step, frozen with stirring, and lyophilized.
As a result of SEM observation of the obtained silica-coated nickel powder, it was confirmed that a silica coating was uniformly formed on the particle surface as in Examples 1 and 4, and that there were substantially no aggregated particles.
[0040]
Comparative Example 1
In Example 1, it carried out like Example 1 except not having performed the vacuum concentration process.
As a result of SEM observation of the obtained powder, it was found from its shape that the surface was not coated with silica at all.
[0041]
Comparative Example 2
In Example 1, the vacuum concentration treatment was continued to remove moisture as it was to obtain a dry powder, and then the same classification operation was performed.
The obtained powder was in a dry state, and a strong agglomerate was generated via the colloidal silica component. Therefore, the agglomeration could not be solved by stirring or ultrasonic irradiation.
[0042]
【The invention's effect】
According to the present invention, a metal-based composite powder that is substantially free of aggregated particles and silica particles, has a uniform and dense silica coating on the surface, and is useful for various applications as a functional powder. Can get well.
[Brief description of the drawings]
FIG. 1 is an SEM photograph of nickel powder before coating.
2 is a SEM photograph of the silica-coated nickel powder obtained in Example 1. FIG.
3 is a SEM photograph of silica-coated nickel powder obtained in Example 3. FIG.
4 is a SEM photograph of silica-coated nickel powder obtained in Example 4. FIG.

Claims (8)

A colloidal silica having a silanol group on the surface and a metallic powder having an average particle size of 0.5 to 500 μm and comprising at least one powder selected from a metal, an alloy, an intermetallic compound and a metal compound. The slurry containing the composition is freeze-dried, and then the obtained dry powder is redispersed in a solvent in which colloidal silica can be dispersed to classify and remove excess colloidal silica that does not contribute to coating. A method for producing a silica-coated metal-based composite powder.   The method for producing a silica-coated metal-based composite powder according to claim 1, wherein the slurry is adjusted to have a viscosity of 0.15 Pa · s or more and freeze-dried in a state where the slurry is maintained.   The method for producing a silica-coated metal-based composite powder according to claim 1 or 2, wherein in the freezing step in freeze-drying, the slurry is cooled and frozen while stirring.   The method for producing a silica-coated metal-based composite powder according to any one of claims 1 to 3, wherein the obtained silica-coated metal-based composite powder is further subjected to a heat treatment at 50 to 1200 ° C.   The method according to any one of claims 1 to 4, wherein the colloidal silica has an average particle size of 1/10 or less of the metal-based powder and 1 to 200 nm.   The method according to any one of claims 1 to 5, wherein a content ratio of the colloidal silica and the metal-based powder in the slurry is a weight ratio of 3:97 to 50:50. The method according to any one of claims 1 to 6 , wherein the slurry containing colloidal silica and metal powder is an aqueous slurry. The method according to any one of claims 1 to 7 , wherein the metal-based powder is nickel.

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