JPH09268014A - Method for treating fine powder surface and surface treated fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an inorganic film on fine powder surface, excellent in uniformity, denseness and bondability to particle surface and obtain functional fine powder improved in characteristics such as dispersibility. SOLUTION: This method for treating fine powder surface is to introduce fine powder with a surface treating solution containing a metal compound as a coating source, and form a coated film, which comprises a degradation product or reaction product of the metal compound, on the fine powder surface by dehydrating, thermally decomposing or reacting the metal compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface-treating fine powder, and more particularly to a method for forming a uniform and dense metal oxide film on the surface of fine powder, and fine powder surface-treated by this method. The method of the present invention is particularly useful for improving the properties of industrially used functional fine powders such as pigments, conductive powders, magnetic powders, and fillers.

[0002]

2. Description of the Related Art The characteristics of functional fine powders, especially the chemical stability such as dispersibility, weather resistance, light resistance, and acid resistance, depend on the product in which the fine powders are used, such as inks, paints, and plastic moldings. It greatly affects the quality of products. Therefore, a fine powder having more excellent characteristics has been demanded, and various processing and finishing treatments have been carried out at the final stage of preparation of the fine powder in order to improve the characteristics. In particular, the surface treatment method of forming a film made of an inorganic and / or organic substance on the surface of particles constituting the fine powder is a useful method for improving the characteristics of the powder.

As a method for forming an inorganic coating on the surface of particles, fine powder to be treated is mixed with water and a soluble salt of metal, and metal oxide or metal hydroxide is deposited on the surface of particles by adjusting pH. Wet processing methods are common.
However, in such a surface treatment method by the wet precipitation method,
There is a problem in the uniformity and denseness of the formed coating film, and the effect of improving dispersibility and the like cannot be exhibited as expected. Also, since the bond between the coating and the base particles is weak, the durability of the coating is poor and deterioration over time is likely to occur.

[0004]

An object of the present invention is to solve the above problems of the prior art and to provide a method for forming an inorganic coating film on the surface of fine particles, which is excellent in uniformity, denseness and bondability to the particle surface. . Another object of the present invention is to provide a functional fine powder having improved properties such as dispersibility by such a method.

[0005]

That is, according to the present invention, there is provided a surface treatment method having the following constitution. (1) When surface-treating fine powder with a metal compound, a surface treatment liquid containing a metal compound as a coating raw material is introduced into a high temperature gas together with the fine powder, and the metal compound is dehydrated, thermally decomposed or reacted on the surface of the fine powder. A surface treatment method for fine powder, characterized by forming a coating film composed of a decomposition product or a reaction product of the metal compound on the surface of the fine powder.

The above surface treatment method includes the following specific embodiments. (2) Forming a metal oxide film on the surface of fine powder (1)
The processing method described in 1. (3) The temperature of the high temperature gas is 100 to 400 ° C.
The processing method described in (1) or (2). (4) The treatment method according to any one of (1) to (3) above, wherein a metal oxide, a metal alkoxide, or a thermally decomposable metal salt is introduced into the high temperature gas. (5) The treatment method according to any one of the above (1) to (4), wherein the raw material metal compound is used in an amount of 0.02 to 5% by weight in terms of oxide, based on the fine powder. (6) The treatment method according to any one of (1) to (5) above, wherein the high temperature gas is oxygen, nitrogen, water vapor or a mixed gas thereof. (7) The treatment method according to any one of (1) to (6), wherein the surface treatment is repeated to form a multi-layer surface coating.

Further, the surface treatment method includes the following treatment method of forming a coating film made of two or more kinds of metal oxides. (8) Using two or more metal compound raw materials, and introducing a surface treatment liquid containing them into a high temperature gas to cause thermal decomposition or reaction to form an oxide film in which the above metals coexist (1) ~ The processing method according to any one of (6). (9) By using two or more kinds of metal compound raw materials and sequentially introducing a surface treatment liquid containing them into a high temperature gas to cause thermal decomposition or reaction, a film in which the above metal oxide is laminated is formed. ) -The processing method in any one of (6).

Further, according to the present invention, the following fine powder having the above surface treatment is provided. (10) A fine powder surface-treated by the method according to any one of (1) to (9) above. (11) The surface-treated fine powder has an average particle size of 0.01 to
1 μm organic or inorganic pigment, conductive powder, filling powder,
The fine powder of (10) above, which is a magnetic powder.

[0009]

[Detailed Description] In the surface treatment method of the present invention, when the surface of a fine powder is treated with a metal compound, a surface treatment liquid containing a metal compound as a coating raw material is introduced into a high temperature gas together with the fine powder to obtain a fine powder. In this method, the metal compound is dehydrated, pyrolyzed or reacted on the surface to form a film of the decomposition product or the reaction product on the surface of the fine powder. Hereinafter, the treatment method of the present invention will be specifically described.

(I) Surface treatment liquid The metal compound as a surface treatment agent needs to be supplied so as to be in uniform contact with the entire powder so that a uniform film is formed. Preferably. Therefore, the solid metal compound dissolves in the surface treatment liquid,
Alternatively, an insoluble substance is used in the form of a slurry suspended in a solution, and a liquid substance is used by diluting it to an appropriate concentration. By using it in a liquid state, it becomes possible to uniformly mix or contact with the fine powder to be treated, and it becomes possible to form a uniform coating.

Although the concentration of the metal compound in the treatment liquid depends on the kind of the compound, it is usually 0.02 to 5% by weight of the treatment liquid.
It is preferably about 0.05 to 2% by weight. If the concentration of the metal compound is lower than this range, the film formation may be insufficient, and if the concentration is higher than this range, it may be difficult to smoothly introduce the treatment liquid especially in the case of suspension or slurry.

The metal compound contained in the surface treatment liquid is a compound which is adsorbed on the surface of the fine powder in a high temperature gas and thermally decomposes or reacts on the surface. In general, a compound that forms a metal oxide, usually a metal oxide or a metal alkoxide or a thermally decomposable metal salt is used. That is, the metal oxide is decomposed in the high temperature gas by dehydration in the high temperature gas, and the metal salt with the oxygen acid is decomposed in the high temperature gas to form a metal oxide coating. The metal halide is also heated in water vapor or in the presence of oxygen to give a metal oxide film.

Examples of metal hydroxides used as raw materials include zinc hydroxide, aluminum hydroxide, silicon hydroxide,
Examples thereof include zirconium hydroxide and titanium hydroxide.
Examples of metal alkoxides include ethyl silicate, aluminum-iso-propoxide, zirconium-tert-butoxide, zirconium-iso-propoxide, titanium tetrabutoxide, titanium tetra-iso-propoxide and the like. Further, as an example of the thermally decomposable metal salt, (a)
Chlorides such as zinc chloride, aluminum chloride, silicon chloride, zirconium chloride and titanium chloride, (b) zinc sulfate, aluminum sulfate, silicon sulfate, zirconium sulfate, sulfates such as titanium sulfate, (c) zinc oxychloride, oxychloride Oxychlorides such as aluminum, silicon oxychloride, zirconium oxychloride, titanium oxychloride, (d) zinc oxysulfate, aluminum oxysulfate, silicon oxysulfate,
Examples thereof include oxysulfates such as zirconium oxysulfate and titanium oxysulfate, and sodium (e) silicate and sodium aluminate. Water or the like is used as the liquid phase component of the surface treatment liquid. An inorganic oxide coating film of titania, alumina, silica, zirconia, zinc oxide or the like is formed on the surface of particles using these metal compounds as raw materials.

(II) Fine Powder Fine powder is an inorganic or organic particle having an average particle size of about 0.01 to 1 μm, and can be processed as long as it is a compound that does not decompose or deteriorate under the processing conditions. .
Specifically, for example, copper azomethine yellow, benzimidazolone yellow, green gold, benzimidazolone orange, phthalocyanine blue, phthalocyanine green, quinacridone red, quinacridone magenta, dioxazine violet, isoindolinone yellow, thioindigo. Bordeaux, organic pigments such as perylene scarlet, titania, silica, alumina, zinc white,
Inorganic pigments such as zirconia and yellow lead, magnetic powders such as manganese, chromium, cerium, palladium, titanium, osmium and platinum, conductive powders such as gold, silver and copper, filler powders such as calcium carbonate, talc and kaolin. To be

(III) Surface Treatment Surface treatment is carried out by introducing a surface treatment liquid containing fine powder and a metal compound as a raw material into a high temperature gas, and heating them in a state of being dispersed in the gas for a short time. . For example,
A mixed slurry of the surface treatment liquid and the fine powder is supplied to the air flow in the presence of a strong air flow such as an air mill or a steam mill, or the treatment liquid is supplied together with the fine powder. These may be sprayed into the container with a hot gas, or a mixed slurry of these, for example,
You may inject into a high temperature gas from a nozzle using a spray dryer etc.

As described above, by introducing the surface treatment liquid containing the metal compound into the high temperature gas together with the fine powder,
The surface of the fine powder particles is uniformly covered with the treatment liquid, and in this state, volatile components (liquid components such as water and volatile components generated by decomposition / reaction of the metal compound) are quickly removed. For this reason, the particles do not aggregate and solidify, and therefore, coating unevenness does not occur and a uniform and dense coating film is formed.

The surface treatment liquid is preferably such that the metal compound in the treatment liquid is 0.0 in terms of oxide based on the weight of the fine powder.
It is supplied so as to be 2 to 5% by weight. If the amount of the metal compound as the surface treatment agent supplied is less than 0.02% by weight, the film formation may be insufficient. In order to obtain a sufficient coating, 0.05% by weight or more is desirable. On the other hand, when the supply amount exceeds 5% by weight, the surface coating becomes unnecessarily thick, the coating effect is saturated, and the coating easily separates, which causes deterioration of the characteristics of the functional fine powder. 2 from the viewpoint of process control stability
% By weight or less is appropriate.

The temperature of the gas is preferably 100 to 400 ° C. If the temperature is less than 100 ° C, the evaporation and removal of liquid components such as solvents and the decomposition of metal compounds do not proceed sufficiently, and the problem remains in the denseness of the coating film, and the remaining liquid components, especially water, cause the deterioration of the powder characteristics. Is not preferable. When the surface treatment liquid and the fine powder are mixed and then introduced, the temperature may be a high temperature of 100 ° C. or higher and a high temperature of 400 ° C. or higher as long as the alteration of the fine powder is not caused, but safety of equipment and energy cost From this point of view, 400 ° C. or lower is preferable. Further, when the surface treatment liquid and the fine powder are separately introduced into the high temperature gas, if the temperature of the gas is too high, the metal compound in the treatment liquid precipitates or decomposes before the two sufficiently contact each other. Will end up. From this point as well, it is desirable to suppress the gas temperature to 400 ° C. or lower in order to obtain a sufficient degree of bonding to the surface of the base particles. From the viewpoint of stable product quality, convenience of equipment and process control, 150 to 300 ° C is more preferable.

As the high temperature gas, oxygen, nitrogen, water vapor or the like or a mixture of two or more kinds thereof (for example, air) is usually used, though it depends on the kind of metal coating to be produced.

By repeating the above surface treatment, a surface coating having a multilayer structure is formed. Further, by using two or more kinds of metal compound raw materials and introducing a surface treatment liquid containing these mixed raw materials into a high temperature gas to cause thermal decomposition or reaction, an oxide film in a state where these metals coexist is formed. can do. Further, a surface treatment liquid containing two or more kinds of metal compound raw materials is sequentially introduced into a high temperature gas to cause thermal decomposition or reaction, whereby a coating film in which these metal oxides are laminated can be formed. Thus, 2
By providing a coating composed of at least one kind of metal oxide,
A surface-treated powder with enhanced functionality can be obtained.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below together with comparative examples. In addition, in each of the following examples, dispersibility and chemical stability were measured and evaluated according to the following test methods. Also,
The percentages and parts representing the component compositions are% by weight and parts by weight, respectively. (1) 40 g of a weather resistance test sample was kneaded with 60 g of melanin-alkyd resin, and a period until the glossiness was reduced to half was measured using a carbon weather meter (manufactured by Ska Testing Machine Co., Ltd.). (2) Acid resistance test (titanium oxide elution test) 1.0 g of titanium oxide pigment as a sample was added to 100% sulfuric acid of 98% concentration.
The amount of titanium oxide eluted was measured by adding it to the solution and maintaining it at 180 ° C. for 1 hour.

Example 1 300 g of titanium oxide fine powder (average particle size 0.27 μ) was added to 70 parts of water.
Mix with 0 g and use a glass bead mill (Bise diameter: 3φ) to make 1
After crushing for 0 minutes, 47.5 g of aluminum sulfate (0.5% in terms of Al ₂ O _{3 with} respect to titanium oxide powder) was added and mixed sufficiently. The obtained mixed slurry is sprayed into a spray dryer (inlet temperature: 200 ° C.) for surface treatment and drying,
A titanium oxide powder pigment whose surface was coated with alumina was obtained. This surface-treated titanium oxide powder was excellent in dispersibility in water and a solvent and hiding power. In addition, when the weather resistance of the surface coating of this powder was examined, it was confirmed that the half-life period of the surface gloss was 15 months, which was significantly longer than the conventional wet-processed powder, and was excellent in weather resistance. It was

Comparative Example 1 (Wet Precipitation Method) The same titanium oxide fine powder as in Example 1 was used, and the powder 300
g, aluminum sulfate 47.5 g and water 700 g were prepared, and 10% sodium hydroxide having a pH of 7 as the end point was added while stirring to deposit hydrous aluminum hydroxide on the particle surface. Then 70
By heating to ℃, to obtain a titanium oxide powder whose surface is coated with alumina. When this alumina-coated titanium oxide powder was subjected to the same weather resistance test as in Example 1, the half-life period of the surface gloss was 10 months.

Example 2 Steam steam inlet steam temperature was 230 ° C. and pressure was 10 kg
/ cm ² and titanium oxide fine powder was added thereto at a rate of 10 kg / min. At the same time, a 20% concentration sodium silicate aqueous solution was quantitatively supplied from another nozzle attached to the steam outlet so that the concentration was 3% in terms of silica based on the weight of titanium oxide. As a result, a titanium oxide powder pigment whose surface was coated with silica was obtained. When the weather resistance and chemical stability of the surface coating of this powder were investigated, the surface gloss half life was 14 months, and the amount of titanium oxide elution was 13%, indicating that the surface gloss half life was longer than that of the conventional wet precipitation method. Is quite long, and the elution amount of titanium oxide is significantly small,
It was confirmed that the coating was very dense and strong.

Comparative Example 2 The same titanium oxide powder as in Example 2 was used, and the powder was 300 g.
Was mixed with 91.5 g of a 20% aqueous sodium silicate solution to prepare a slurry, and 10% sulfuric acid having a pH of 7 was gradually added with stirring to precipitate hydrous silica on the powder surface. Then, this was heated to 80 ° C. to obtain a titanium oxide powder having a silica coating on the surface.
This powder was examined for weather resistance and chemical stability of the surface coating in the same manner as in Example 2. As a result, the half life of the surface gloss was 8 months, and the elution amount of titanium oxide was 35%.

Example 3 A high-temperature air mill which maintained an air flow of 15 kg / cm ² at 150 ° C.
Titanium oxide fine powder was charged into the (shock crusher) at a rate of 15 kg / min. In parallel with this, a 50% ethyl silicate aqueous solution was added to the titanium oxide in an amount of 0.4% in terms of silica.
Was sprayed from the nozzle at a rate corresponding to, to perform surface treatment and pulverization of titanium oxide. As a result, a titanium oxide powder pigment whose surface was coated with silica was obtained. When the chemical stability of the surface coating of this powder was examined, the elution amount of titanium oxide was 15%, which was significantly smaller than that of the conventional wet precipitation method.

Comparative Example 3 Using the same titanium oxide powder as in Example 3, 300 g of the powder was used.
And 48% of a 50% concentration ethyl silicate aqueous solution corresponding to 0.4% in terms of silica relative to titanium oxide are mixed to prepare a slurry, and 10% hydrochloric acid is added with pH 7 as the end point while stirring to obtain hydrous silica. Was gelled to form a film on the surface of titanium oxide. Then, this was heated to 80 ° C. to obtain a titanium oxide powder whose surface was coated with silica.
When the chemical stability of the surface coating of this powder was examined, the elution amount of titanium oxide was 33%.

Example 4 Steam steam inlet steam temperature was 260 ° C. and pressure was 12 kg.
/ cm ² and titanium oxide fine powder was added thereto at a rate of 10 kg / min. At the same time, from another nozzle attached to the steam outlet, an aluminum sulfate aqueous solution having a concentration of 20% becomes 1% in terms of alumina to the weight of titanium oxide, and ethyl silicate in terms of silica to the weight of titanium oxide. An amount of 2% was supplied in a fixed amount. As a result, a titanium oxide powder pigment having a film having a uniform composition of silica and alumina formed on its surface was obtained. When we examined the weather resistance and chemical stability of the surface coating for this powder,
The half life of surface gloss is 24 months, the elution amount of titanium oxide is 20%, the half life of surface gloss is much longer than that of similar products by the conventional wet precipitation method, and the elution amount of titanium oxide is significantly large. It was confirmed that the film was very small and very dense and strong.

Comparative Example 4 300 g of the same titanium oxide powder as in Example 4 was coated with alumina on the surface in the same manner as in Comparative Example 1,
Further, for this powder, a silica coating was formed on the surface of the alumina coating in the same manner as in Comparative Example 3. When the weather resistance and chemical stability of the surface coating of this powder were examined, the period of half reduction of surface gloss was 15 months, and the elution amount of titanium oxide was 41%. In Comparative Example 1 or 3, an attempt was made to form a film having a uniform composition of silica and alumina by using aluminum sulfate and ethyl silicate at the same time. It was difficult to obtain an oxide film in which silica that had been precipitated in step 1 was simultaneously precipitated, and the target surface-treated titanium oxide powder could not be obtained.

Example 5 300 g of titanium oxide powder was mixed with 700 g of water, and this was crushed for 10 minutes using a glass bead mill to obtain a slurry. Meanwhile, a mixed solution of tin alkoxide and antimony alkoxide was prepared. Next, the slurry and the mixed solution were mixed at 200 ° C. so that 10% by weight of tin alkoxide in terms of tin oxide and 1% by weight of antimony oxide in terms of antimony oxide were supplied to the titanium oxide powder.
Was directly introduced into a spray drier under the conditions described above to perform surface treatment and drying to obtain a conductive titanium oxide powder having a surface coating made of antimony-doped tin oxide. This powder was kneaded with a soft vinyl chloride resin so as to have a weight of 50% to obtain a sheet having a thickness of 1 mm. As a result of measuring the surface resistance of this sheet, it was 1 × 10 ⁸ Ω, and it was possible to confirm the conductivity equivalent to that of the conventional wet-processed conductive powder. That is, by using the conductive powder obtained by the treatment method of the present invention, it is possible to manufacture a conductive sheet having a similar level of conductivity at a lower cost than conventional ones.

By the way, in the conventional surface treatment by the precipitation method, in order to form a tin oxide film doped with antimony, these are simultaneously precipitated from a mixed solution of tin and antimony alkoxide, but the film is not uniform. Yes, and costly.

Example 6 300 g of titanium oxide powder was mixed with 700 g of water, and this was crushed for 10 minutes using a glass bead mill to obtain a slurry. In addition, the titanium oxide powder was converted to silica in an amount of 0.
Water glass in an amount of 5% by weight was added. This prepared slurry was introduced into a spray dryer at an inlet condition of 200 ° C., surface treatment and drying were performed, and a titanium oxide powder having a surface coated with silica was obtained. The surface-treated titanium oxide powder was mixed with pulp and various fillers, and the yield of the mixture was measured using an 80 mesh sieve yield tester, which is an important item in the papermaking test. As a result, the yield amount was 76%. On the other hand, the same yield amount was measured for the titanium oxide powder having the silica coating obtained in Comparative Example 51.
%, Which is significantly smaller than that of the present example, and that the product subjected to the surface treatment of the present invention was confirmed to be superior in dispersibility to that of the conventional treatment method.

Example 7 A cadmium sulfate solution (Cd: 150 g / l) and an aqueous sodium sulfide solution (Na ₂ S: 22 g / l) were mixed and reacted in equivalent amounts, washed, filtered and dried, and then at 560 ° C. for 5 hours. Baked. This was ground to give a cadmium sulfide yellow pigment. Next, the steam at the inlet of the steam mill was set to 220 ° C. and the pressure was set to 10 kg / cm ² , and the above cadmium sulfide pigment was added at a rate of 10 kg / min. In parallel with this, from another nozzle attached to the steam outlet, ethyl silicate was supplied in a fixed amount in a mixed solution of 0.1% by weight in terms of silica to cadmium sulfide, and after surface treatment, it was dried. It was As a result, silica was uniformly and densely coated on the powder surface to obtain cadmium sulfide powder having excellent dispersibility.

The surface-treated yellow cadmium sulfide pigment (product of the present invention) and the surface-untreated pigment (control example) were kneaded in a polyethylene resin with 0.1 parts and 1.0 part of titanium oxide, respectively. Then, the dispersibility was compared under the same conditions. As a result, the product of the present invention had a coloring power of 120% with respect to the untreated product.

[0035]

According to the surface treatment method of the present invention, a uniform and dense inorganic compound film can be formed on the surface of fine particles, so that the dispersibility and chemical stability of fine powder can be effectively improved. You can Further, the treatment method of the present invention can be carried out at low cost regardless of the type of the base particles, and is therefore particularly effective for improving the characteristics of various functional fine powders.

Claims (11)

[Claims] 1. When surface-treating a fine powder surface with a metal compound, a surface treatment liquid containing a metal compound as a coating raw material is introduced into a high temperature gas together with the fine powder, and the metal compound is dehydrated and thermally decomposed on the surface of the fine powder. Alternatively, a fine powder surface treatment method is characterized in that a film made of a decomposition product or a reaction product of the metal compound is formed on the fine powder surface by reacting. 2. The processing method according to claim 1, wherein a metal oxide film is formed on the surface of the fine powder. 3. The processing method according to claim 1, wherein the temperature of the high temperature gas is 100 to 400 ° C. 4. The treatment method according to claim 1, wherein a metal oxide, a metal alkoxide or a thermally decomposable metal salt is introduced into the high temperature gas. 5. The treatment method according to claim 1, wherein the raw material metal compound is used in an amount of 0.02 to 5% by weight in terms of oxide based on the fine powder. 6. The processing method according to claim 1, wherein the high temperature gas is oxygen, nitrogen, steam or a mixed gas thereof. 7. The treatment method according to claim 1, wherein the surface treatment is repeated to form a multilayer surface coating. 8. An oxide film coexisting with the above-mentioned metals is formed by using two or more kinds of metal compound raw materials and introducing a surface treatment liquid containing them into a high temperature gas to cause thermal decomposition or reaction. The processing method according to any one of 1 to 6. 9. A coating film in which the above-mentioned metal oxide is laminated is formed by using two or more kinds of metal compound raw materials and sequentially introducing a surface treatment liquid containing them into a high temperature gas to cause thermal decomposition or reaction. Item 7. The processing method according to any one of Items 1 to 6. 10. A fine powder surface-treated by the method according to claim 1. 11. The fine powder according to claim 10, wherein the fine powder to be surface-treated is an organic or inorganic pigment having an average particle diameter of 0.01 to 1 μm, a conductive powder, a filling powder, and a magnetic powder.