JP5173245B2 - Method for producing surface-coated zinc oxide - Google Patents

Description

  The present invention relates to a method for producing zinc oxide having a particle surface coated.

Zinc oxide is used in various applications such as white pigments, UV shielding materials, adsorbents, photocatalysts, catalysts, and is actively used as UV shielding materials for cosmetics, paints, plastics, papers, etc. .
Ultraviolet rays are roughly divided into three regions A, B, and C in order of increasing wavelength. Since the ultraviolet rays in the C region having a wavelength of 200 to 290 nm are shielded by the ozone layer, in general, skin damage such as sunburn and inflammation is caused by the A region having a wavelength of 320 to 380 nm and the B region having a wavelength of 290 to 320 nm. It is said that. It is said that ultraviolet rays in the B region, so-called UVB, have the greatest effect on the skin, and conventionally, sunscreen cosmetics have been focused on protecting the skin from UVB. On the other hand, ultraviolet rays in the A region, so-called UVA, have a gentle effect on the skin compared to UVB, but are contained in a large amount in sunlight, and because they are highly permeable, they easily cause damage in the deep part of the skin. In recent years, attention has also been paid to UVA shielding ability.
Various inorganic oxides are used as materials having UVA shielding ability. Among them, zinc oxide is excellent in protecting the skin from UVA, has high visible light transparency and transparency, and is tanned. Widely used as an ultraviolet shielding material used in cosmetics. As a method for producing such zinc oxide, for example, (1) a method in which metal zinc is heated and melted and evaporated and then oxidized (so-called French method), and (2) a reducing agent is added to the zinc-containing ore and fired. A method (so-called American method), (3) a method in which a zinc salt is neutralized in a solution, and a neutralized product is solid-liquid separated and calcined. (4) After the neutralization is produced, hydrolysis is performed in a medium. There are known a method, (5) a method in which zinc oxide and carbon dioxide gas are reacted in a solution, and the obtained basic carbonate is solid-liquid separated and fired. ((1) to (4) are disclosed in Non-Patent Document 1, (4) is disclosed in Patent Document 1, and (5) is disclosed in Patent Document 2.)
However, zinc oxide has a relatively high solubility in water as an inorganic oxide, and has a disadvantage that zinc oxide is easily eluted in an aqueous solvent used in cosmetics. In addition, since zinc oxide has a high photocatalytic activity, it also has a problem of decomposing and altering organic components such as oils and surfactants contained in cosmetics. For this reason, a dense amorphous silica coating is preferably applied by adhering a separate coating of at least two different hydrated metal oxides such as silica, titania, alumina, zirconia, etc. to the zinc oxide particle surface. A technique (Patent Document 3) is known in which zinc oxide is inactivated by coating with alumina. In addition, the surface of zinc oxide is coated with an oxide or hydroxide of Al, Si, Zr, Sn (Patent Document 4), or coated with high-density silica (Patent Document 5), thereby improving water elution. Techniques for suppressing or suppressing the photocatalytic activity are known.

"Chemical products of 14096", published by Chemical Industry Daily, January 24, 2006, P48-P49 JP-A-4-164815 JP 2001-342021 A JP-A-8-104823 Japanese Patent No. 2851885 Japanese Patent Laid-Open No. 11-302015

  When the surface of zinc oxide particles is coated with silica or the like using the techniques described in Patent Documents 3 to 5, although the photocatalytic activity of zinc oxide is reduced and the water elution property is suppressed, it is not sufficient but further. There is a need for improvement. However, as described in Non-Patent Document 1 and Patent Document 2 described above, zinc oxide produced by vapor phase oxidation or baking causes sintering of particles, and dry powder causes consolidation of particles. . For this reason, when coating the surface of silica or the like, the zinc oxide is difficult to disperse in an aqueous medium, and even when dispersed, it is easy to agglomerate due to the addition of silica or the like. Is difficult to form, and further improvement such as suppression of water elution cannot be obtained.

As a result of intensive studies to solve these problems, the present inventors have produced spherical zinc oxide particles in an aqueous medium and then dried the obtained spherical zinc oxide particles in a gas phase. The present inventors have found that water elution can be further improved by coating with an inorganic compound in an aqueous medium without performing a heating operation such as firing.

That is, the present invention includes a step of obtaining spherical zinc oxide particles by reacting a zinc compound with a neutralizing agent in an aqueous medium at 60 ° C. or more and 100 ° C. or less without containing an iron compound and / or a cobalt compound , This is a method for producing a surface-coated spherical zinc oxide particle comprising a step of coating an inorganic compound on the surface of the obtained spherical zinc oxide particle in an aqueous medium without heating the resulting spherical zinc oxide particle. In addition, the step of obtaining spherical zinc oxide particles includes a method of producing finely divided zinc oxide that hardly aggregates by setting the reaction temperature, the addition time of the neutralizing agent, and the like.

  In the zinc oxide obtained in the present invention, the photocatalytic activity is suppressed, and in particular, the water elution amount of zinc can be suppressed low. For this reason, it is useful as an ultraviolet shielding material 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 blending of non-aqueous solvents such as oils can be reduced. Can be set freely.

  The present invention is a method for producing a surface-coated zinc oxide, wherein a zinc compound is reacted with a neutralizing agent in an aqueous medium to obtain zinc oxide particles, and the obtained zinc oxide particles are dried in a gas phase. The surface of the particles is coated with an inorganic compound in an aqueous medium without performing a heating operation such as firing. In the present invention, since the heating operation is not performed in the gas phase, since the inorganic compound is coated in a dispersed state without sintering the zinc oxide particles, a uniform coating layer is easily formed, and excellent water elution properties The improvement effect is obtained.

  The reaction between the zinc compound and the neutralizing agent includes (1) adding a neutralizing agent to the aqueous zinc compound solution, and (2) adding the aqueous zinc compound solution and the neutralizing agent to the aqueous medium in parallel. (3) A zinc compound aqueous solution is added to an aqueous medium containing a neutralizing agent. In the present invention, the method (1) in which the particle diameter and particle shape are easily controlled is preferred. 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. The neutralizing agent to be reacted with these is appropriately selected according to the properties of the zinc compound. For example, in the case of an acidic zinc compound, alkali metal or alkaline earth metal hydroxide such as sodium hydroxide, potassium hydroxide or calcium hydroxide, alkali metal or alkaline earth metal carbonate such as sodium carbonate or potassium carbonate, etc. Basic compounds such as salts, ammonium compounds such as ammonia, ammonium carbonate, and ammonium nitrate can be used. In addition, for basic zinc compounds, inorganic acids such as sulfuric acid and hydrochloric acid, organic acids such as acetic acid and formic acid, and the like can be used.

  When the average particle diameter of the zinc oxide particles to be generated (50% cumulative diameter by electron microscopy) 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 The range of 0.05 μm is more preferable. There is no particular limitation on the shape of the zinc oxide particles, spherical particles such as true spheres and substantially spheres, regular particles such as needle-shaped, spindle-shaped, plate-shaped, and flake-shaped anisotropic shaped particles, agglomerated particles, etc. The irregularly shaped particles can be used, but the spherical shape is particularly preferable. A reaction temperature of 60 ° C. or higher is preferable because spherical particles are easily generated and the neutralized product is easily hydrolyzed. There is no particular upper limit to the reaction temperature, but if it is 100 ° C. or lower, no special equipment such as a pressure vessel is required, which is industrially preferable. In the case of the method (1), it is preferable to set the addition time of the neutralizing agent in the range of 10 to 40 minutes because spherical zinc oxide particles having an average particle diameter in the above range can be easily obtained. If the addition time is shorter than the above range, anisotropically shaped particles are likely to be formed, and if longer, the particles grow. A more preferable range is 10 to 30 minutes. The amount of the neutralizing agent used may be a neutralizing equivalent to the zinc compound, and preferably the neutralizing agent is slightly excessive.

  The obtained zinc oxide particles are subjected to a coating step of an inorganic compound without performing a heating operation in the gas phase, and the temperature and pH are adjusted appropriately while maintaining the temperature and pH at which the zinc oxide particles are produced. The coating process can be performed. Moreover, after removing the soluble salts produced | generated at the manufacturing process of a zinc oxide particle, it is preferable to use for the coating process of an inorganic compound. As the method, (1) the aqueous slurry in which the zinc oxide particles are produced is filtered and washed to remove soluble salts, and the solid oxide separated zinc oxide particles are 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. Further, depending on the agglomeration degree of the zinc oxide particles, it may be appropriately dispersed using a wet pulverizer such as a vertical sand mill, a horizontal sand mill, or a ball mill. Further, the concentration of the zinc oxide particles in the aqueous slurry is not particularly limited, and is appropriately set according to production equipment, production capacity, etc., but is preferably in the range of 5 to 200 g / liter, and 20 to 100 g / liter industrially. The range of is more preferable.

  Examples of the inorganic compound to be coated on the particle surface include metal oxides and phosphates. The inorganic compound may be a laminate of two or more, or may be coated as a mixture, or a coating when two or more are used. There is no limit to the order. 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 an industrially most preferable aspect, since productivity is inhibited when a large amount of silica is coated, (A) a coating layer containing titania is formed, and silica is coated thereon, preferably a coating layer containing porous silica. Or (B) a coprecipitate coating layer containing titania and silica is eliminated. As described above, when silica and titania are used in combination, the coating amount of silica is preferably in the range of 10 to 50% by weight in terms of SiO ₂ with respect to zinc oxide, and titania is 0.5 in terms of TiO _{2 with} respect to zinc oxide. A range of ˜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.

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 zinc oxide particles. 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 each inorganic compound species, for example, the method described in Japanese Patent Application No. 2006-276517 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 Japanese Patent Application No. 2006-276518 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 compounds used in these methods, and sodium silicate, potassium silicate, silica sol, and the like can be used for the silicon compound. Water-soluble compounds such as 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. 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.

  After forming the coating of the inorganic compound, if necessary, it is filtered and washed to separate it into solid and liquid, followed by drying and dry pulverization to obtain a zinc oxide powder having a coated surface. 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.

  In the present invention, an organic compound may be further coated for the purpose of imparting dispersibility to a solvent, a paint, plastics, or the like, and may preferably be coated on an inorganic compound coating. As a method for coating an organic compound, (1) a method in which zinc oxide 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) Examples include a method of bringing zinc oxide and an organic compound into contact 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) organic aluminum compound (aluminum chelate, etc.), (c) organic zirconium compound (carboxylic acid ester 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.), (5) 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 in the range of 0.1 to 50% by weight and more preferably in the range of 0.1 to 30% by weight with respect to zinc oxide.

  The surface-coated zinc oxide obtained in the present invention is particularly used by blending with an ultraviolet shielding composition. Specific examples of the ultraviolet shielding composition include sunscreen cosmetics, cosmetics such as basic cosmetics, paints, plastics, and the like. In addition to the conventional components used for these, an appropriate amount of the surface-coated zinc oxide is included. Used in combination. For example, for cosmetics, in addition to the surface-coated zinc oxide, known components commonly used in cosmetics, such as (1) solvents (water, lower alcohols, etc.), (2) oil agents (higher fatty acids, higher grades) Alcohols, organopolysiloxanes (silicone oil), hydrocarbons, oils and fats), (3) surfactants (anionic, cationic, amphoteric, nonionic, etc.), (4) humectants (glycerins) (5) Organic ultraviolet absorbers (benzophenone derivatives, paraaminobenzoic acid derivatives, salicylic acid derivatives, etc.), (6) antioxidants (phenolic, organic acids, etc.) Or salts thereof, acid amides, phosphates, etc.), (7) thickeners, (8) fragrances, (9) colorants (pigments, dyes, dyes, etc.), (10) physiologically active ingredients (vita) Emissions, hormones, 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 amount of surface-coated zinc oxide in the cosmetic is preferably in the range of 0.1 to 50% by weight.

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

Example 1
(Synthesis of zinc oxide particles)
168 g of zinc sulfate (ZnSO ₄ .7H ₂ O) was dissolved in pure water to prepare a 100 g / liter aqueous solution in terms of ZnO. After heating 250 ml of this aqueous solution to a temperature of 90 ° C. and maintaining at 90 ° C., 283 ml of a 200 g / liter sodium hydroxide solution was added over 15 minutes with stirring to obtain a neutralized product. And aged for 90 minutes. Subsequently, it filtered and wash | cleaned and obtained the zinc oxide particle (sample a).

(Inorganic compound coating)
50 g of zinc oxide particles (sample a) obtained without heating operation in the gas phase was redispersed in pure water using an ultrasonic disperser to prepare a 100 g / liter aqueous slurry. After heating 500 ml of this aqueous slurry to a temperature of 70 ° C., a 50 g / l aqueous solution of titanium tetrachloride corresponding to 5% by weight as TiO ₂ and a 10% sodium hydroxide solution were stirred, and the pH was 8.0. The first coating layer containing titania was formed by simultaneous addition over 40 minutes so as to be in the range of ˜9.5. In this state, it was aged by holding for 60 minutes.
Subsequently, the slurry temperature was cooled to 50 ° C., 50 g / liter sodium silicate aqueous solution corresponding to 25% by weight as SiO ₂ was added over 40 minutes, and the mixture was stirred for 20 minutes. It added over 40 minutes and neutralized so that it might become the range of 0-9.5, and the 2nd coating layer containing porous silica was formed. In this state, the mixture was aged for 20 minutes, adjusted to pH in the range of 8.0 to 8.5, filtered, washed, dried, and dry pulverized to obtain titania / silica-coated zinc oxide (sample A). .

Comparative Example 1
(Synthesis of zinc oxide particles)
An aqueous slurry having a concentration of about 7% in terms of ZnO was prepared by dispersing 40 g of zinc oxide powder as a primary reagent in pure water. After raising the temperature of 265 ml of this aqueous slurry to a temperature of 45 ° C., carbon dioxide was blown into the slurry until the pH of the slurry reached about 6.0 while stirring to produce basic zinc carbonate. The obtained basic zinc carbonate was filtered, washed and dried, then calcined at a temperature of 320 ° C. for 45 minutes, and then dry pulverized to obtain zinc oxide particles (sample b).

(Inorganic compound coating)
50 g of the obtained zinc oxide particles (sample b) were redispersed in pure water using an ultrasonic disperser to prepare a 100 g / liter aqueous slurry. A comparative titania / silica-coated zinc oxide (sample B) was obtained in the same manner as in Example 1 except that this aqueous slurry was used.

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. Zinc oxide (Samples A and B) of Example 1 and Comparative Example 1 was dispersed in 100 milliliters of pure water in which 1.0 g of each was adjusted to pH 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. The results are shown in Table 1. It was found that the zinc oxide obtained in the present invention was superior in zinc water elution as compared with the comparative sample.

The present invention can suppress zinc elution of zinc oxide into an aqueous solvent, and can be used for various applications such as a white pigment, an ultraviolet shielding material, an adsorbent, and a catalyst.
In addition, by using fine particles of zinc oxide, it is excellent in ultraviolet shielding ability and transparency, and thus is useful as an ultraviolet shielding material to be blended in cosmetics, paints, plastics, paper and the like.

Claims (3)

A step of obtaining spherical zinc oxide particles by reacting a zinc compound with a neutralizing agent in an aqueous medium at 60 ° C. or higher and 100 ° C. or lower without containing an iron compound and / or a cobalt compound, and the obtained spherical zinc oxide particles A surface-coated spherical shape comprising a step of coating at least one inorganic compound selected from silica, titania, alumina, and zirconia on the particle surface in an aqueous medium without heating in a gas phase. A method for producing zinc oxide. The method for producing spherical zinc oxide according to claim 1, wherein a neutralizing agent is added to the zinc compound solution over 10 to 40 minutes. 2. The method for producing spherical zinc oxide according to claim 1, wherein the obtained spherical zinc oxide particles are filtered and washed and then redispersed in an aqueous medium to coat the inorganic compound.