JP2010132493A - Composite powder and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a fine zinc oxide more easily at a low cost, which is suitable for mass production. <P>SOLUTION: By allowing a silicon compound to be present when a zinc compound is precipitated by an alkali in water of 50°C or above, a fine zinc oxide having a BET specific surface area of 30-100 m<SP>2</SP>/g is obtained. The product is a composite powder of a coprecipitate containing zinc oxide and silica, and has sufficient ultraviolet ray-shielding capacity, transparency or the like since it contains zinc oxide. The content of zinc in the coprecipitate is preferably 70.0-99.9 wt.% in terms of ZnO. This method does not need special equipment such as a mill and a mixer in the case of reaction which becomes a high viscosity, and therefore mass production is possible. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a composite powder containing zinc oxide and a method for producing the same. Moreover, it is related with the ultraviolet-ray shielding composition containing the said composite powder, and sunscreen cosmetics.

Zinc oxide is used in various applications such as white pigments, ultraviolet shielding agents, adsorbents, photocatalysts, catalysts, etc., and is particularly excellent in ultraviolet shielding ability, and also has high transparency to visible light and excellent transparency. Used in cosmetics, paints, plastics, papers, etc. The finer the zinc oxide, the higher the effects such as ultraviolet shielding ability and transparency, and therefore there is a demand for finer zinc oxide.
Such fine zinc oxide, for example, in Patent Document 1, a zinc salt aqueous solution and an alkaline aqueous solution are separately and simultaneously in an amount ratio such that the equivalent ratio of zinc: alkali is 1: 1 to 1: 3. The reaction vessel is continuously or semi-continuously charged, and the reaction vessel is continuously stirred at a rotational speed of 2000 to 20000 rpm for reaction, and the neutralized product produced in this reaction is continuously or semi-continuously reacted. The method is described in which it is removed from the reaction vessel and then filtered, washed, then dried and fired.

  On the other hand, when zinc oxide becomes finer, it tends to aggregate and the dispersibility in a solvent tends to be lowered. In addition, the solubility in water becomes relatively high, and elution easily occurs in an aqueous solvent used in cosmetics and the like. In addition, since the catalytic activity becomes high, there is a problem that organic components such as oils and surfactants contained in cosmetics are decomposed or altered. For this reason, fine zinc oxide is modified or coated with silica or the like to improve the above problem. For example, in Patent Document 2, a dispersion containing silica sol having a primary particle diameter of 1 to 150 nm and fine zinc oxide or zinc oxide sol having a primary particle diameter of 1 to 1000 nm are mixed, and then the pH of the solution is changed. It describes that a zinc oxide / silica composite is produced by coagulating and precipitating silica and zinc oxide simultaneously. Patent Document 3 covers the surface of fine zinc oxide with Al, Si, Zr, Sn oxides or hydroxides to suppress catalytic activity, and Patent Document 4 covers high-density silica. It describes that water elution is suppressed by doing.

JP-A-10-120418 WO02 / 024153 pamphlet Japanese Patent No. 2851885 Japanese Patent Laid-Open No. 11-302015

In the method of the above-mentioned Patent Document 1, an ultrafine zinc oxide having a specific surface area of 30 to 100 m ² / g can be produced, but a special apparatus such as an impeller mill or an in-line mixer is used in the reaction that results in a high viscosity. Therefore, it is difficult to apply the method to mass production, and a method for manufacturing more easily and inexpensively is desired. In addition, although the silica treatment described in Patent Documents 2 to 4 improves the dispersibility of zinc oxide, water elution, catalytic activity, etc., the zinc oxide particles are already aggregated during the silica treatment. For these reasons, it is difficult to obtain a sufficient effect by the silica treatment.

As a result of various studies aimed at producing fine zinc oxide more easily and inexpensively, the present inventors have found that silicon compounds are present when zinc compounds are precipitated with alkali in water. As a result, it was found that fine zinc oxide having a BET specific surface area of 30 to 100 m ² / g was obtained, and that it had sufficient ultraviolet shielding ability, transparency, etc., and the present invention was completed.

That is, the present invention is a composite powder having a BET specific surface area of 30 to 100 m ² / g and comprising a coprecipitate of zinc and silicon, and the silicon compound and the zinc compound are alkalinized in water at 50 ° C. or higher. And a method for producing a composite powder characterized by coprecipitation.

The composite powder of the present invention has excellent transparency and ultraviolet shielding ability. Moreover, this composite powder suppresses the catalytic activity of zinc oxide, and can keep the amount of zinc eluted in water low. For this reason, it is useful as an ultraviolet shielding agent to be blended in cosmetics, paints, plastics, paper, etc., and since the amount of zinc elution into an aqueous solvent is low, the amount of a non-aqueous solvent such as an oil can be reduced Can be set freely.
In addition, the composite powder manufacturing method of the present invention does not require a special device such as a mill or a mixer in the case of a reaction having a high viscosity, so that it can be applied to mass production, and is manufactured more easily and inexpensively. can do.

The present invention is a composite powder having a BET specific surface area of 30 to 100 m ² / g and comprising a coprecipitate of zinc and silicon. Zinc can be a compound such as zinc oxide and zinc hydroxide, but those having an X-ray diffraction peak of zinc oxide are preferred, and all zinc components are more preferably zinc oxide. Silicon can be a compound such as silica (silicon oxide) or silicate, but is difficult to identify by X-ray diffraction. The composite powder is preferably fine, and is in the range of 30 to 100 m ² / g in terms of BET specific surface area. When the average particle diameter (50% cumulative diameter by electron microscopy) of the composite powder is in the range of 0.001 to 0.1 μm, the ultraviolet shielding ability and transparency are excellent, and preferably 0.005 to 0.05 μm. The thing of the range of is more preferable. The zinc content in the composite powder is preferably in the range of 70 to 99.9% by weight in terms of ZnO, and more preferably in the range of 90 to 99.9% by weight. If the zinc content is less than the above range, it is not preferable because it is difficult to obtain the effect of zinc such as ultraviolet ray shielding ability. On the other hand, if the zinc content is more than the above range, the silicon content is reduced, and the fine composite powder is not preferable. Since it is difficult to obtain a body, it is not preferable. The composite powder of zinc and silicon can be observed with an electron microscope, and the amount can be measured by a usual method such as fluorescent X-ray analysis or ICP emission analysis.

  The particle surface of the composite powder may be coated with an inorganic compound. Examples of the inorganic compound to be coated include metal oxides, phosphates, and the like, and the inorganic compound may be a laminate of two or more, or may be coated as a mixture. There is no limit. Further, the properties of the coating layer may be porous or dense. As the inorganic compound, at least one metal oxide selected from silica, titania, alumina, zirconia, and the like is preferable because the effect of suppressing the elution of zinc from water is large, and the effect of silica is particularly preferable. The metal oxide in the present invention is a compound including an anhydrous metal oxide, a hydrous oxide, a hydrated oxide, and a hydroxide. The coating amount of the inorganic compound can be appropriately set according to the coating type and purpose, and is preferably about 0.1 to 50% by weight with respect to zinc oxide.

As the most industrially preferable aspect, when a large amount of silica is coated, the handling work and the production efficiency are reduced due to the thixotropic viscosity of the treated slurry and cake, and the productivity is hindered. Therefore, (A) When a coating layer containing titania is formed and silica is formed thereon, preferably a coating layer containing porous silica is formed, or (B) a coating layer of coprecipitate containing titania and silica is formed. Such a problem is solved. When silica and titania are used in combination as described above, the silica coating amount is preferably in the range of 10 to 50% by weight in terms of SiO ₂ with respect to the composite powder, and titania is 0 in terms of TiO _{2 with} respect to the composite powder. The range of 5 to 20% by weight is preferred. If the silica coating amount is less than the above range, it is difficult to obtain the desired zinc water-elution property and the effect of suppressing the photocatalytic activity of zinc oxide and titania. This is not preferable because it is difficult to obtain the improvement effect. In addition, if the amount of titania coating is less than the above range, it is difficult to improve the decrease in productivity due to the use of silica, and even if it is increased, further improvement is difficult to obtain. On the other hand, the photocatalytic activity by titania may increase. Therefore, it is not preferable. A more preferable silica coating amount is in the range of 20 to 50% by weight, and more preferably in the range of 25 to 40% by weight. A more preferable range of the titania coating amount is 1 to 10% by weight.

  In the present invention, it is important that a silicon compound is present when the zinc compound is precipitated in water with an alkali, and at least a part of the silicon compound present co-precipitates and precipitates together with the zinc compound. Silicon compounds and zinc compounds are used in the state dissolved in water, and the presence of silicon compounds during precipitation of zinc suppresses the formation of anisotropically shaped particles such as rods and flakes of zinc particles. And a fine coprecipitate is obtained. To add a zinc compound, a silicon compound and an alkali into water, (1) a method of adding a zinc compound and an alkali into water containing a silicon compound, (2) into a water containing a silicon compound and a zinc compound, A method of adding an alkali; (3) a method of adding an alkali and a silicon compound in water containing a zinc compound; (4) a method of adding a mixed solution of an alkali and a silicon compound in water containing a zinc compound; (5) Method of adding zinc compound and silicon compound to water containing alkali, (6) Method of adding zinc compound, silicon compound and alkali to water, (7) Alkali and silicon compound in water And a method of adding a zinc compound and the like. One of the methods (1) to (7) is appropriately selected, or two or more of these methods are combined. Rukoto can also. In the present invention, the methods (1) and (7) are preferred because the particle diameter and particle shape can be easily controlled. Although the addition time of a zinc compound, a silicon compound, and an alkali can be set suitably, since it is easy to obtain a desired coprecipitate when it is the range for 10 minutes-2 hours, it is preferable. When adding 2 or more types in water, it is preferable to add each in parallel. The usage-amount of an alkali should just be about 1.0 to 3 times with respect to the neutralization equivalent of a zinc compound, Preferably it is about 1.5 to 2.5 times. Moreover, it is preferable to add a zinc compound, a silicon compound, an alkali, etc., maintaining the pH of water in the range of 9.5 to 12.0, and the range of 10 to 11 is more preferable. The temperature of the water at the time of addition may be room temperature or may be heated to about 30 to 50 ° C., but the temperature of the water at the time of reacting the zinc compound and the alkali is preferably 50 ° C. or more. The zinc compound can be hydrolyzed to generate zinc oxide. Further, the temperature of water is more preferably 70 ° C. or higher, further preferably 80 ° C. or higher, and a fine composite powder having a nearly spherical shape can be obtained. Furthermore, the preferable temperature of water is 85-105 degreeC.

As the silicon compound to be used, water-soluble compounds such as sodium silicate and potassium silicate are preferably used. As sodium silicate, sodium orthosilicate, sodium sesquisilicate, sodium metasilicate and the like can be used, and sodium silicate No. 1 (SiO ₂ / Na ₂ O molar ratio is 2) which is an aqueous solution of sodium silicate, No. 2 (SiO ₂ / Na ₂ O molar ratio is 2.5), No. 3 (SiO ₂ / Na ₂ O molar ratio is 3), No. 4 (SiO ₂ / Na ₂ O molar ratio is 4), N special sodium silicate (SiO ₂ / Na ₂ O molar ratio: 3.80 to 4.10), C special sodium silicate (SiO ₂ / Na ₂ O molar ratio: 3.30 to 3.50), AP silicate (SiO ₂ / Na ₂ O molar ratio: 4.25 to 4.45) (all manufactured by Nippon Kagaku Kogyo Co., Ltd.) can be preferably used, and SiO ₂ / Na ₂ O molar ratio. Use sodium silicate of 3 or more Preferred for sodium content remaining is less. Zinc compounds include known compounds such as acidic zinc compounds such as zinc sulfate, zinc chloride and zinc nitrate, and basic zinc compounds such as zinc carbonate, and are not particularly limited. Examples of the alkali include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide and calcium hydroxide, alkali metals or alkaline earth metal carbonates such as sodium carbonate and potassium carbonate, ammonia Basic compounds such as ammonium compounds such as ammonium carbonate and ammonium nitrate can be used.

  After co-precipitation, if necessary, the pH and temperature may be maintained for about 10 minutes to 5 hours for aging. Thereafter, while stirring, the aqueous solution is preferably heated to 50 ° C. or higher, more preferably about 60 to 250 ° C., and still more preferably about 80 to 110 ° C., to increase the crystallinity of zinc. Moreover, the obtained coprecipitate may be subjected to filtration and washing, solid-liquid separation, drying at a temperature of about 50 to 200 ° C., and dry pulverization, if necessary. Moreover, you may bake the obtained coprecipitation dry material at the temperature of about 200-800 degreeC. For the solid-liquid separation, a filter such as the above-described filter press or roll press can be used. Band type heaters, batch type heaters, spray dryers, etc. are used for drying, impact pulverizers such as hammer mills, pin mills, roller mills, pulverizers, crushers such as crushers, roll crushers, etc. A compression crusher such as a jaw crusher, an airflow crusher such as a jet mill, or the like can be used.

  The obtained coprecipitate is subjected to a coating step of an inorganic compound as necessary, and the coating step is performed while maintaining the temperature and pH at which the coprecipitate was produced or by appropriately adjusting the temperature and pH. Can do. Moreover, after removing the soluble salts produced | generated at the manufacturing process of a coprecipitate, it is preferable to use for the coating process of an inorganic compound. As the method, (1) the aqueous slurry in which the coprecipitate is produced is filtered and washed to remove soluble salts, and the solid-liquid separated coprecipitate is redispersed in an aqueous medium to obtain an aqueous slurry. (2) It is possible to remove soluble salts from the aqueous slurry in the liquid phase without performing solid-liquid separation by ion exchange membrane dialysis, electrodialysis, etc., and industrially suitable for mass production (1) This method is preferred. For filtration and washing, a filter such as a filter press or a roll press can be used. The concentration of the coprecipitate in the aqueous slurry is not particularly limited and is appropriately set according to the production equipment, production capacity, etc., but is preferably in the range of 5 to 200 g / liter, and in the range of 20 to 100 g / liter. Is more preferable.

  The inorganic compound may be coated by a known method. If the metal oxide is coated, the compound containing the metal element constituting the metal oxide and the neutralizing agent are added to the aqueous slurry containing the coprecipitate. The coating layer can be formed by adding them separately or simultaneously in parallel. If the compound containing the metal element is acidic, it is preferable to perform the latter simultaneous addition while maintaining the pH of the aqueous slurry in the vicinity of neutrality so that zinc does not elute. Although a more specific operation method varies depending on the individual inorganic compound species, for example, the method described in JP-A-2008-94917 is preferable for forming the coating layer (A). That is, in an aqueous slurry of zinc oxide particles, the titanium compound is neutralized in the range of pH 8.0 to 10.0, and then the silicon compound is added to neutralize the pH in the range of 8.0 to 10.0. It is a method to do. The method described in JP-A-2008-94646 is preferable for forming the coating layer (B). That is, this is a method in which a titanium compound and a silicon compound are added in an aqueous slurry in the range of pH 8.0 to 10.0. Water-soluble compounds such as titanium chloride and titanium sulfate are preferably used for the titanium compound used in these methods, and the above compounds can be preferably used for the silicon compound. As the neutralizing agent, the above acidic compound or basic compound is appropriately selected and used according to the titanium compound or silicon compound to be used.

For coating with the inorganic compound, it is preferable to coat the slurry of the coprecipitate with carboxylic acid and / or a salt thereof, and then add the inorganic compound. The carboxylic acid is a compound having a carboxyl group and can be used without limitation. For example, the following can be used, and citric acid and / or a salt thereof are particularly preferable.
(1) Polycarboxylic acids, particularly dicarboxylic acids and tricarboxylic acids such as oxalic acid and fumaric acid.
(2) Hydroxypolycarboxylic acids, especially hydroxydi- or hydroxytri-carboxylic acids such as malic acid, citric acid or tartronic acid.
(3) (Polyhydroxy) monocarboxylic acid, such as glucoheptonic acid or gluconic acid.
(4) Poly (hydroxycarboxylic acid) such as tartaric acid.
(5) Dicarboxyl amino acids and their corresponding amides, such as aspartic acid, asparagine or glutamic acid.
(6) A hydroxylated or non-hydroxylated monocarboxyl amino acid such as lysine, serine or threonine.
As the carboxylate, any salt can be used without limitation. For example, alkali metal salts such as sodium and potassium, ammonium salts and the like can be used.

  The coprecipitate may be further coated with an organic compound for the purpose of imparting dispersibility to a solvent, paint, plastics, or the like, and may preferably be coated on a coating of an inorganic compound. As the organic compound coating method, (1) a method in which a coprecipitate is solid-liquid separated from an aqueous slurry, dried, and then contacted with an organic compound in a gas phase using a dry pulverizer or a high-speed stirrer (2 ) A method of bringing a coprecipitate and an organic compound into contact with each other in an aqueous slurry. In general, the method (1) has a good yield of the organic compound, and the method (2) can be uniformly coated. Therefore, the method is appropriately selected according to the kind of the organic compound. Examples of the organic compound used include (1) organosilicon compounds ((a) organopolysiloxanes (dimethylpolysiloxane, methylhydrogen polysiloxane, methylmethoxypolysiloxane, methylphenylpolysiloxane, dimethylpolysiloxanediol, dimethylpolysiloxane) Dihydrogen and the like or copolymers thereof), (b) organosilanes (amino silane, epoxy silane, methacryl silane, vinyl silane, mercapto silane, chloroalkyl silane, alkyl silane, fluoroalkyl silane, etc. or their hydrolysis products ), (C) organosilazanes (hexamethylsilazane, hexamethylcyclotrisilazane, etc.), (2) organometallic compounds ((a) organotitanium compounds (aminoalkoxytitanium, phosphates) Tertitanium, carboxylic acid ester titanium, sulfonic acid ester titanium, titanium chelate, phosphite titanium complex, etc.), (b) organoaluminum compound (aluminum chelate, etc.), (c) organozirconium compound (carboxylate zirconium, zirconium) Chelate etc.), (3) polyols (trimethylolpropane, trimethylolethane, pentaerythritol etc.), (4) alkanolamines (monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, Tripropanolamine) or derivatives thereof (organic acid salts such as acetate, oxalate, tartrate, formate, benzoate, etc.), (5) higher fatty acids (stearic acid, lauric acid) Oleic acid etc.) or metal salts thereof (aluminum salt, zinc salt, magnesium salt, calcium salt, barium salt etc.), (6) higher hydrocarbons (paraffin wax, polyethylene wax etc.) or derivatives thereof (perfluorinated products etc.) These organic compounds may be used singly or in combination of two or more, and when used in cosmetics, it is preferable to use organopolysiloxanes and higher fatty acids. The coating amount of the organic compound is preferably from 0.1 to 50% by weight, more preferably from 0.1 to 30% by weight, based on the coprecipitate.

  The composite powder obtained in the present invention is particularly used by blending with an ultraviolet shielding composition. Specific examples of the UV shielding composition include sunscreen cosmetics, cosmetics such as basic cosmetics, paints, plastics, etc. In addition to the conventional ingredients used for them, the composite powder is blended in an appropriate amount. Used. For example, for cosmetics, in addition to the composite powder, known components that are usually used in cosmetics, such as (1) solvents (water, lower alcohols, etc.), (2) oil agents (higher fatty acids, higher alcohols) , Organopolysiloxanes (silicone oil), hydrocarbons, oils and fats), (3) surfactants (anionic, cationic, amphoteric, nonionic, etc.), (4) humectants (glycerins, Polyols such as glycols, non-polyols such as pyrrolidone carboxylic acids) (5) organic ultraviolet absorbers (benzophenone derivatives, paraaminobenzoic acid derivatives, salicylic acid derivatives, etc.), (6) antioxidants (phenolic, organic acids or (7) thickeners, (8) fragrances, (9) colorants (pigments, pigments, dyes, etc.), (10) physiologically active ingredients (vitamins, Rumon, amino acids, etc.), (11) an antibacterial agent or the like may be blended. The form of the cosmetic is not particularly limited, such as solid, liquid, or gel. In the case of liquid or gel, the dispersion may be any of a water-in-oil emulsion, an oil-in-water emulsion, and an oil type. The blending amount of the composite powder in the cosmetic is preferably in the range of 0.1 to 50% by weight.

  The composite powder obtained in the present invention was 2.91% by weight of composite powder using a binder of liquid paraffin / petroleum / stearic acid = 40 / 26.7 / 1 (weight ratio) as described later in Evaluation 2. When the transmittance of the coating film prepared by blending is measured, the visible light transmittance at a wavelength of 550 nm is 97% or more, the ultraviolet transmittance at a wavelength of 350 nm is 55% or less, and a wavelength of 300 nm is obtained. A coating film having an ultraviolet transmittance of 50% or less can be produced, and if it is such, it can be used as a coating composition having sufficient transparency and ultraviolet shielding properties.

  Examples of the present invention are shown below, but the present invention is not limited thereto.

Example 1
An aqueous solution of sodium silicate is heated to a temperature of 90 ° C., and an aqueous solution of zinc sulfate (ZnSO ₄ .7H ₂ O) and an aqueous solution of sodium hydroxide are taken over 40 minutes while maintaining the temperature and the pH range of the aqueous solution of 10-11. And co-precipitate (sample a) was obtained by aging for 30 minutes, followed by filtration and washing.
A portion of this sample a was collected, dried and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 99% by weight of zinc oxide and 1% by weight of silica. The BET specific surface area was 55.2 m ² / g. As a result of observation with an electron microscope, the composite particles were nearly spherical, and no large rod-like particles were observed.

Example 2
In Example 1, except that the amount of sodium silicate was increased 5 times, the same treatment as in Example 1 was performed to obtain a coprecipitate (sample b).
A portion of this sample b was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 95% by weight of zinc oxide and 5% by weight of silica. The BET specific surface area was 51.0 m ² / g. As a result of observation with an electron microscope, the composite particles were nearly spherical, and no large rod-like particles were observed.

Example 3
In Example 1, it processed like Example 1 except having increased the quantity of sodium silicate 30 times, and obtained the coprecipitate (sample c).
A portion of this sample c was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 70% by weight of zinc oxide and 30% by weight of silica. The BET specific surface area was 62.2 m ² / g. As a result of observation with an electron microscope, the composite particles were nearly spherical, and no large rod-like particles were observed.

Example 4
After heating the water to a temperature of 90 ° C., a zinc sulfate (ZnSO ₄ · 7H ₂ O) aqueous solution, an aqueous sodium silicate solution and an aqueous sodium hydroxide solution were added simultaneously over 40 minutes while maintaining the temperature. Thereafter, aging was carried out for 30 minutes, and then the pH was adjusted to 7 with sulfuric acid, followed by filtration and washing to obtain a coprecipitate (sample d).
A part of this sample d was collected, dried and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 70% by weight of zinc oxide and 30% by weight of silica. The BET specific surface area was 84.9 m ² / g. As a result of observation with an electron microscope, the composite particles were nearly spherical, and no large rod-like particles were observed.

Example 5
In Example 1, the aqueous solution of sodium silicate was heated to a temperature of 80 ° C., and the same operation was performed as in Example 1 except that the temperature was maintained, thereby obtaining a coprecipitate (sample e).
A portion of this sample e was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 99% by weight of zinc oxide and 1% by weight of silica. The BET specific surface area was 47.5 m ² / g. As a result of observation with an electron microscope, the composite particles were nearly spherical, and no large rod-like particles were observed.

Example 6
In Example 1, an aqueous solution of sodium silicate was heated to a temperature of 70 ° C., and the same operation was performed as in Example 1 except that the temperature was maintained, thereby obtaining a coprecipitate (sample f).
A part of this sample f was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 99% by weight of zinc oxide and 1% by weight of silica. The BET specific surface area was 41.5 m ² / g. As a result of observation with an electron microscope, it was a fine composite particle close to a sphere, but formation of a part of rod-like particles was observed.

Example 7
In Example 1, the aqueous solution of sodium silicate was heated to a temperature of 60 ° C., and the same operation was performed as in Example 1 except that the temperature was maintained, thereby obtaining a coprecipitate (sample g).
A part of this sample g was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 99% by weight of zinc oxide and 1% by weight of silica. The BET specific surface area was 40.3 m ² / g. As a result of observation with an electron microscope, formation of a large number of rod-shaped particles was observed.

Example 8
In Example 1, the aqueous solution of sodium silicate was heated to a temperature of 50 ° C., and the same operation was performed as in Example 1 except that the temperature was maintained, thereby obtaining a coprecipitate (sample h).
A part of this sample h was collected, dried, and subjected to analysis. As a result, it was a composite powder of zinc and silicon and showed an X-ray diffraction peak of zinc oxide, but no other peaks were observed. It was. The coprecipitate contained 99% by weight of zinc oxide and 1% by weight of silica. The BET specific surface area was 33.6 m ² / g. As a result of observation with an electron microscope, formation of a large number of rod-shaped particles was observed.

Example 9
The coprecipitate (sample a) obtained in Example 1 was redispersed in pure water using an ultrasonic disperser to prepare a 100 g / liter aqueous slurry. An aqueous citric acid solution was added to the aqueous slurry, the pH was adjusted to 9.5 to 10.0 with sulfuric acid, the temperature was raised to 50 ° C., and then an aqueous sodium silicate solution corresponding to 10% by weight as SiO ₂ And sulfuric acid were added over 40 minutes while maintaining the pH at 9.5 to 10.0 and stirred for 30 minutes, and then the sulfuric acid aqueous solution was added over 40 minutes so that the pH was in the range of 8.0 to 8.5. And then neutralized to form a coating layer containing silica. After aging for 30 minutes in this state, filtration, washing, drying, and dry pulverization were performed to obtain a silica-coated composite powder (sample A).
In Sample A, it was confirmed that a silica coating layer of 10% by weight was formed.

Comparative Example 1
Zinc oxide particles (sample i) were obtained in the same manner as in Example 1 except that water containing no sodium silicate was used instead of the aqueous solution of sodium silicate used in Example 1.
A part of this sample i was collected, dried and subjected to analysis. As a result, it showed an X-ray diffraction peak of zinc oxide, and it was found to be zinc oxide. Further, the BET specific surface area was 31.1 m ² / g. As a result of observation with an electron microscope, a large number of rod-like particles were observed.

Comparative Example 2
A silica-coated zinc oxide powder (Sample I) was obtained in the same manner as in Example 9, except that Sample i obtained in Comparative Example 1 was used instead of Sample a used in Example 9.

Samples obtained in the examples (samples a to h) were observed with an electron microscope, and as a result of the BET specific surface area, fine zinc oxide having a high specific surface area was obtained as compared with the sample obtained in the comparative example (sample i). It was also found that the particle shape was nearly spherical and the production of rod-like particles was suppressed.
Further, when the amount of zinc dissolved in water was measured in the following evaluation 1, it was found that the samples a and b were almost the same as the comparative sample i, but the sample c was reduced to about half. Moreover, it turned out that the amount of water elution of sample A is reduced to 1/30 of sample a.
Evaluation 1 (Evaluation of water elution)
In the present invention, in order to promote water elution of the sample, the water resistance was evaluated based on the elution amount of zinc in the strongly acidic aqueous solution. The samples of Examples and Comparative Examples were each dispersed in 100 ml of pure water whose pH was adjusted to 3 with sulfuric acid. After 1 minute, the dispersion was centrifuged, and the zinc concentration in the resulting supernatant was measured by atomic absorption analysis.

Using the samples (a to h, A) obtained in Examples and a binder of liquid paraffin / petroleum / stearic acid = 40 / 26.7 / 1 (weight ratio) as in Evaluation 2 described later, Sample 2. When the transmittance of the coating film containing 91% by weight was measured, the visible light transmittance at a wavelength of 550 nm was 97% or more, the ultraviolet transmittance at a wavelength of 350 nm was 55% or less, and a wavelength of 300 nm was obtained. It was found that the ultraviolet transmittance was 50% or less. From this, it was found that the samples (a to h, A) can be used as a coating composition having sufficient transparency and ultraviolet shielding properties.
Evaluation 2 (Measurement results of optical characteristics)
The sample was made into the paste which assumed cosmetics by the method described below. This paste was applied onto a transparent triacetate film using a doctor blade so that the film thickness was about 25 μm, and then air-dried for 30 minutes. The ultraviolet / visible spectral transmittance spectrum of this coating film was measured using a spectrophotometer (manufactured by Shimadzu Corporation, UV-VIS UV2200A type) equipped with an integrating sphere.
(Paste formulation)
Sample 1.2g
Binder (liquid paraffin / petroleum / stearic acid = 40 / 26.7 / 1 (weight ratio)) 40.0 g
Glass beads 50.0g
(Paste preparation method)
The formulation was charged into a 140 cm ³ lidded glass bottle, sealed, and then dispersed using a paint conditioner (Red Devil (USA), Quick Mill).

  Since the composite powder of the present invention has excellent transparency and ultraviolet shielding ability, it is useful as an ultraviolet shielding agent to be blended in cosmetics, paints, plastics, paper and the like. It can also be used for various applications such as white pigments, adsorbents, and catalysts.

2 is an electron micrograph (25,000 times) of a sample a obtained in Example 1. FIG. 2 is an X-ray diffraction chart of Sample a obtained in Example 1. FIG. 2 is an electron micrograph (25000 times) of the sample b obtained in Example 2. 3 is an X-ray diffraction chart of Sample b obtained in Example 2. FIG. 4 is an electron micrograph (25,000 times) of the sample c obtained in Example 3. 6 is an X-ray diffraction chart of sample c obtained in Example 3. FIG. 4 is an electron micrograph (25,000 times) of a sample d obtained in Example 4. 6 is an X-ray diffraction chart of a sample d obtained in Example 4. 4 is an electron micrograph (25000 times) of the sample e obtained in Example 5. 6 is an X-ray diffraction chart of a sample e obtained in Example 5. It is an electron micrograph (25000 times) of the sample f obtained in Example 6. 7 is an X-ray diffraction chart of a sample f obtained in Example 6. It is an electron micrograph (25000 times) of the sample g obtained in Example 7. 7 is an X-ray diffraction chart of sample g obtained in Example 7. FIG. 4 is an electron micrograph (25,000 times) of the sample h obtained in Example 8. 6 is an X-ray diffraction chart of a sample h obtained in Example 8. 2 is an electron micrograph (25,000 times) of the sample i obtained in Comparative Example 1. 3 is an X-ray diffraction chart of Sample i obtained in Comparative Example 1.

Claims (10)

A composite powder having a BET specific surface area of 30 to 100 m ² / g and comprising a coprecipitate of zinc and silicon. The composite powder according to claim 1, which has an X-ray diffraction peak of zinc oxide. The composite powder according to claim 1 or 2, wherein the content of zinc in the coprecipitate is in the range of 70.0 to 99.9 wt% in terms of ZnO. The composite powder according to claim 1, wherein the surface of the coprecipitate has a coating of an inorganic compound. A method for producing a composite powder, wherein a silicon compound and a zinc compound are coprecipitated with an alkali in water at 50 ° C or higher. The method for producing a composite powder according to claim 5, wherein a silicon compound, a zinc compound, and an alkali are added to water at 50 ° C. or higher. The method for producing a composite powder according to claim 5, wherein a zinc compound and an alkali are added to water containing a silicon compound at 50 ° C. or higher. The composite powder according to any one of claims 5 to 7, wherein the zinc compound and the silicon compound are co-precipitated while maintaining the pH of water in the range of 9.5 to 12.0. Production method. The ultraviolet shielding composition containing the composite powder as described in any one of Claims 1-4. A sunscreen cosmetic comprising the composite powder according to any one of claims 1 to 4.

Images