WO2007119993A1

WO2007119993A1 - Reforming method of the surface of inorganic particles

Info

Publication number: WO2007119993A1
Application number: PCT/KR2007/001833
Authority: WO
Inventors: Sang Hoon Jeon; Sun Sang Kwon; Se Jun Park; Seung Hwan Yi; Min Kyung Shim; Yeong Jin Choi; Han Sung Kim; Duck Hee Kim; Ih Seop Chang
Original assignee: Amorepacific Corporation
Priority date: 2006-04-14
Filing date: 2007-04-16
Publication date: 2007-10-25

Abstract

The present invention relates to a method for modifying the surface of inorganic particles. More particularly, it relates to a method of etching the surface of inorganic particles by treatment with a suitable concentration of acid using a high-energy source, a method of modifying the surface of the inorganic particles etched according to said etching method, with a coating material, and a method of forming structures on the surface synthetic mica using a suitable concentration of acid under controlled reaction conditions. When inorganic particles are treated using said methods, the glossiness of the inorganic particles themselves can be reduced and the properties-in-use thereof can be improved.

Description

[DESCRIPTION]

[invention Title]

REFORMING METHOD OF THE SURFACE OF INORGANIC PARTICLES [Technical Field]

The present invention relates to a method for modifying the surface of inorganic particles, and more particularly to a method of etching the surface of inorganic particles by treatment with a suitable concentration of acid using a high-energy source, a method of modifying the surface of the inorganic particles etched according to said etching method, with a coating material, and a method of forming structures on the surface synthetic mica using a suitable concentration of acid under controlled reaction conditions.

[Background Art]

Inorganic pigments in cosmetics are largely divided, according to function, into a coloring pigment, a white pigment, an extender pigment and a functional pigment. The coloring pigment serves to adjust the color tone of products, and the white pigment can control covering powder in addition to the color tone. The extender pigment serves to adjust the color tone with a thinner and, at the same time, to adjust the properties-in-use (spreadability, adhesion, etc.) or glossiness of products. Also, it is used to maintain the formulation of products. In addition, the functional pigment blocks UV light and has various effects of increasing the usability or effect of products.

Of the inorganic pigments used in cosmetics, the extender pigments include talc, kaolin, mica and the like. Among them, mica is largely produced in various rocks or clays, includes a number of species and is found in various forms ranging from large hexagonal plates reaching a crystal size of 20 cm or more to those having clay size.

One in which a hydroxyl group (-0H) in the crystal of natural mica is substituted with fluorine (F) is synthetic mica. The crystal structure of synthetic mica is formed of tetrahedrons of SiO₄ as base units, like natural mica. Between the two upper and lower tetrahedral layers, ions (Mg²⁺, Li⁺, etc.) showing an octagonal arrangement are ionically bonded, thus forming a sandwich structure of tetrahedron-octagon-tetrahedron. This sandwich structure is called "tablet". The tablets are layered on each other. Between the tablet layers, alkali metal or alkaline earth metal ions are weakly ionically bonded as "interlayer ions" . In general, synthetic mica used in cosmetics is non- swelling mica containing, for example, K⁺, has properties like those of natural muscovite and phlogopite. Particularly, because synthetic mica contains a very small amount of Fe components, which are contained in natural mica in large amounts, it has high whiteness and clear gloss. Also, the crystal particle size can be controlled according to the kind of a solvent and temperature conditions for crystallization and can be prepared in the form of flake-like fine powder with size of 0.1~l//m. Such flake-like synthetic mica powder shows soft touch, spreadability and good adhesion to the skin, and thus properties required in cosmetics. Also, because synthetic mica is obtained by substituting the hydroxy1 group (-OH) of natural mica with a fluoride group (-F), the crystal structure of the tablet layers in synthetic mica is strong, and synthetic mica has increased strength and heat resistance compared to natural mica.

Generally, prior foundation or powder raw materials contain highly refractive pigments, such as talc, TiO₂ and Fe₂O₃, such that these pigments can increase covering power and adjust skin color tone. However, these highly covering pigments have problems in that they tend to make makeup thick, make hair follicles visible to the eye but have no skin transparency, and leave an unnatural finish. Also, these inorganic pigments have problems in that they originally have low brightness or saturation, and when they are wet in water or sebum, the brightness or saturation thereof will further be reduced to make a makeup film dark and to reduce makeup effects.

Meanwhile, the beauty of skin appearance is greatly influenced by skin denseness . As the skin becomes denser, light is uniformly reflected from the skin, and skin transparency increases. Suitable examples of cosmetics that present this dense skin include prior cosmetics, which use covering action caused by a light scattering effect, and a transparent, flake-like powder having excellent adhesion to the skin.

Accordingly, in order to maximally use the pure transparency of synthetic mica among inorganic pigments and the characteristics of the scale-like smooth surface of the synthetic mica, there have been efforts to examine a method for preparing products having high particle uniformity in high aspect ratio and to develop cosmetic raw materials, which have good gloss or transparency and can present a dense skin. However, such transparency or glass imposes limitations on the use of mica in pact formulations. The scale-like smooth surface of mica tends to present glossiness instead of giving transparency, shows darkness due to a change in color after make-up application, thus reducing make-up lasting properties. Thus, the use of mica in pact formulations is limited, unlike other formulations. Also, mica has a low ability to absorb sebum, and thus is easily wet even in a small amount of sebum, so that the color thereof becomes dark. This phenomenon is a problem common in plate-like inorganic pigments.

In an actual make-up film, the secretion of sweat is also not negligible. In a high-temperature and high- humidity environment in the rainy season or summer season, in which a large amount of sweat is secreted, sebum and sweat interact with each other. When the amount of sebum in a make-up film is excessive, the make-up film is separated while it is admixed with sebum. Also, a large amount of sweat flows to push the flowable make-up film, thus promoting the breakdown of make-up. To increase the sebum-absorbing capability of mica, a method of coating mica with a surface-treating substance, such as dimethicone or triethoxycarprylylsilane, has been used, but it was not easy to solve problems associated with the inherent glossiness of mica. Thus, mica materials having a relatively low glossiness have been used, but have encountered limitations. Also, a method for solving the glossiness of mica materials while maintaining the sensory feel thereof is still not developed. [Disclosure]

[Technical Problem]

It is an object of the present invention to provide inorganic particles (including mica) , which have controlled glossiness and improved properties-in-use by modifying the surface thereof with a suitable concentration of acid using a high energy source .

Another object of the present invention is to provide inorganic particles, which have improved oil absorption, whiteness and water repellency by coating inorganic particles etched by acid.

Still another object of the present invention is to provide synthetic mica, which has reduced glossiness resulting from the use of controlled acid concentration and reaction conditions and has increased oil absorption so as to prevent make-up breakdown caused by sebum absorption. [Technical Solution]

To achieve the above objects, in one aspect, the present invention provides a method for modifying the surface of inorganic particles by acid treatment using a high-energy source, the method comprising the steps of: (1) adding inorganic particles to an acid and stirring the mixture to prepare a slurry; and (2) applying a high-energy source to the slurry, and then washing, filtering, drying and then crushing the inorganic particles. In another aspect, the present invention provides a method for modifying the surface of inorganic particles by acid treatment using a high-energy source, the method additionally comprising, after the step (2) of said method, (3) a step of coating the crushed inorganic particles with a coating material.

In still another aspect, the present invention provides a method for forming structures on the surface of synthetic mica, the method comprising the steps of: (1) treating the surface of synthetic mica with an acid; (2) aging the acid-treated mica at 30-40 ^°C for 30 minutes to 2 hours to form structures on the surface of the synthetic mica .

Hereinafter, the present invention will be described in further detail.

An etching process used in the present invention is a process used in semiconductor manufacturing. In semiconductor manufacturing, it refers to a process in which a photoresist pattern formed in a photo process is used as a mask to treat the underlying film. The etching process is divided, according to an etching method, into wet etching and dry etching. Because the dry etching can become a problem in terms of productivity in the case of flake-like inorganic particles, it is preferable to use the wet etching in a point of view of a cosmetic raw material.

For etching, an acid is generally used, and H⁺ is a strong oxidizing agent which shows high reactivity.

In the etching process, in the case of a mixture with other ions, like mica, it is important to know etchants and etching rates for many materials in order to understand a selective etching tendency.

Generally, the etching of Si is performed using HF with high selectivity. Also, the etching of SiO₂ is performed using HF (+H₂O) . As the source of HF, NH₄F is used in order to a given level of [H⁺] as shown in the following equation. [Equation 1]

NH₄F -> NH, + HF SiO; + 6HF -> H₂ + SiF_s + 2H₂O

Herein, the etching rate is influenced by the concentration of HF, etching time, the amount of energy in acid treatment, and reaction temperature. An increase in the concentration of HF leads to an increase in etching depth and width, and an increase in etching time or reaction temperature leads to an increase in etching degree.

Also, when structure particles are produced from a buffered liquid in a process of lowering temperature after acid treatment, the production rate of the particles becomes fast.

Moreover, Si₃N₄ can be etched by phosphoric acid and shows an etching rate of 180 A/minute at 180 ^°C .

In addition, aluminum is etched by a mixture of phosphoric acid, nitric acid and acetic acid as shown in equation 2 below. [Equation 2] FhPO₊ + CH₁COOH + HNO₃ + H₂O (-3O⁰C) 6H+ + 2Al —> 3H₂ + 2Al'^* (Al-'" is water-boluble)

Also, when only silicon exists, nitric acid along with HF is used as shown in the following equation 3. [Equation 3]

HF + HNO_., + H₂O

3Si + 4HNO, -, 3SiO₂ + 4NO + 2H₂O 3SiO₂ + 1 SHF → 3H₂SiF₆ + 6H₂O

In this case, the reactants are transferred to the surface of silicon, react selectively on the substrate to be etched, and leave the reaction surface.

Meanwhile, in order for the etching process, which is used in semiconductor manufacturing, to be applied in the present invention, the following problems should be solved.

First, in semiconductor manufacturing, a single material is used as a material to be etched, but in the present invention, a mineral such as mica is used as a material to be etched. Thus, this problem can be solved by setting reaction conditions based on the fact that etchants and reaction conditions are different between semiconductor process and the present invention.

Second, the size of a substrate is different between semiconductor manufacturing and the present invention. The size of a substrate used as inorganic particles is significantly as small as a few tens of microns. Thus, the tendency of etching of an inorganic particle substrate such as mica should be examined through a pre-test. Also, mild conditions such as low concentration should be selected as HF etching conditions in order to prevent the substrate from being overetched. Hereinafter, the method for modifying the surface of inorganic particles by acid treatment using a high energy source will be described in detail.

(1) Step of adding inorganic particles to an acid and stirring the mixture to prepare a slurry

At least one acid for treating inorganic particles is placed in a slurry reactor, and then fine inorganic particles are added little by little to the acid, such that they do not come in contact with the reactor wall. At this time, for complete wetting, the mixture is subjected to mechanical stirring for 30 minutes to prepare a slurry.

The acid used in this step is at least one acid selected from the group consisting of hydrofluoric acid, nitric acid, acetic acid, hydrochloric acid and phosphoric acid. The concentration of the acid is preferably 1-20 wt%. This is because the etching of inorganic powder should be performed in conditions milder than etching in the semiconductor manufacturing field in order to prevent overetching from occurring. Also, at the set concentration of the acid, the slurry is prepared in a concentration of 1-50 wt%. The concentration of the slurry is determined depending on the bulk density and wetting volume of the substrate . (2) Step of applying a high energy source to the slurry, and then washing, filtering, drying and crushing the inorganic particles

In this step, the high energy source is at least one selected from among heating, microwave and plasma. Herein, the level of energy is determined between 200-1000 W, and the method for treating the slurry is determined depending on the kind of inorganic particles and the concentration of the acid. At an energy higher than 1000 W, overetching can occur, and at an energy lower than 200 W, etching does not sufficiently occur. The inorganic particles thus treated is washed, filtered, dried and then crushed.

(3) Step of coating the crushed inorganic particles with a coating material . The inorganic particles, the surface of which was etched in the step (2), are coated with a coating material. The reason why the surface of the inorganic particles is modified with the coating material is because, in a high- temperature and high-humidity environment in the rainy season or summer season, when the amount of sebum in a make-up film is excessive, the make-up film is separated while it is admixed with sebum, a large amount of sweat is secreted to push the flowable make-up film, thus promoting the breakdown of make-up. For this reason, the surface of the inorganic particles is coated with the coating material, such that the oil absorption, whiteness or water repellency can be improved.

The coating material (surface-treating agent) used in the present invention may be at least one selected from the group consisting of dimethicone, methicone, triethoxy caprylylsilane, acrylate/tridecyl/triethoxysilylpropyl methacrylate/dimethicone methacrylate copolymer, and triethoxysilylethyl polydimethyl siloxyethylhexyl dimethicone.

Each of the coating materials is used in an amount of 1-5 wt% based on the total weight of the composition according to the formulation thereof. Polysiloxane has a very low surface tension, and treatment therewith imparts excellent hydrophobicity and lubricity to the substrate. It has excellent water repellency and has no surface activity, and thus is widely used as a surface-treating agent. Silane is a surface-treating agent having a very good reactivity, because the Si-O bond thereof readily reacts with water to form silanol . It is lipophilic, is readily dispersed in esters, mineral oils and silicone fluids, and has good water repellency. An acrylate- silicone copolymer has increased compatibility with oils and esters due to the addition of acrylate, compared to silicone. It has excellent adhesion to the skin, shows long-lasting effects caused by high water repellency and forms an elastic, non-sticky film.

In another aspect, the present invention provides inorganic particles for cosmetics, which have surfaces modified by acid treatment using a high energy source.

The acid, which is used to provide the inorganic particles for cosmetics, is specifically at least one acid selected from the group consisting of hydrofluoric acid, nitric acid, acetic acid, hydrochloric acid and phosphoric acid, and the acid is used at a concentration of 1-20 wt%. The high energy source is at least one selected from among heating, microwave and plasma. Herein, the level of energy- is determined between 200-1000 W, and the method for treating the slurry with the high energy source is determined depending on the kind of inorganic particles and the concentration of the acid. At the energy of more than 1000 W, overetching can occur, and at the energy of less than 200 W, etching does not sufficiently occur. The present invention provides a method for forming a structure on the surface of synthetic mica among inorganic particles. The method will not be described in detail.

(1) Step of treating the surface of synthetic mica with an acid

At least one acid for treating inorganic particles is placed in a slurry reactor, and then fine inorganic particles are added little by little to the acid, such that they do not come in contact with the reactor wall . At this time, for complete wetting, the mixture is subjected to mechanical stirring for 30 minutes to prepare a slurry.

The acid used in this step is specifically at least one selected from the group consisting of hydrofluoric acid, nitric acid, acetic acid, hydrochloric acid and phosphoric acid. Herein, the concentration of acid for forming a suitable structure is preferably 2-6 wt%. If the concentration of the acid is less than 2 wt%, etching by the acid will not be observed, and if it exceeds 6 wt%, non-selective etching will occur in the case of flake-like inorganic powder, leading to overetching. At the set concentration of the acid, the slurry is prepared at a concentration of 5-20 wt%, and the energy of 500-1000 J/ml is applied, and the method for treating the synthetic mica is determined depending on the kind of synthetic mica and the concentration of the acid. At an energy lower than 500 J/ml, surface structures will not be observed, and at an energy higher than 1000 J/ml, the surface structures will be agglomerated to show a irregular shape. (2) Step of aging the acid-treated synthetic mica at 30- 40 ^°C for 30 minutes to 2 hours to form structures on the surface of the synthetic mica

In a process of lowering the temperature of the slurry after the above acid treatment, structures are formed on the surface of the synthetic mica. Specifically, ions, including Si⁴⁺, O^2', F^" and K⁺, from tetrahedral structures on the surface etched by the acid, form structures having silicon dioxide (SiO₂) or potassium- fluorosilicate (K₂SiFg) as a framework, in a buffered reaction solution.

In the process of forming the surface structures according to the present invention, as aging time becomes longer, the size of crystals during the formation of the structures becomes larger. The aging time, which shows regular surface structures, such as a spherical shape, a rod shape and a star shape, is between 30 minutes and 2 hours after the acid treatment. Thus, the aging time suitable for forming the surface structures according to the present invention is 30 minutes to 2 hours. Also, if the amount of energy applied in the acid treatment of step (a) is 500 J/ml , a spherical surface structure will be formed, and if it is 1000 J/ml, a cross- shaped surface structure will be formed. In the above- described conditions, the surface structures are formed in the order of spherical, rod-shaped, L-shaped, star-shaped, cross-shaped and octahedral -shaped structures on the surface of synthetic mica. With the passage of time, the structures, which are formed on the surface of synthetic mica, are changed from a single shape to a composite shape.

(3) Step of wet-coating, dry-coating or vapor-coating the synthetic mica surface having the structures formed thereon, with a coating material at 80-150^°C In this step (3) , the surface of synthetic mica, having the structures formed thereon, is wet -coated, dry- coated or vapor-coated with a coating material. The wet coating is performed after the powder is wetted with the coating material, and the coating amount is controlled through filtering and drying. The dry coating is carried out in a mill by introducing the coating material in an amount corresponding to the coating amount . In the vapor coating, the powder is fluidized in a reactor with high flow rate, and the coating material is added to the powder through a temperature-controlled nozzle at a temperature above the boiling temperature thereof, so that the powder and the coating material react with each other in the vapor state. Thus, the vapor coating is used to form a uniform thin film. This coating process is performed for 2 hours at 80-150 ^°C depending on the kind of coating material. The drying temperature is substantially the same as the reaction temperature for coating.

In the present invention, the coating material used in the step (3) may be at least one selected from the group consisting of dimethicone, methicone, triethoxy caprylylsilane, acrylate/tridecyl/triethoxysilylpropyl methacrylate/dimethicone methacrylate copolymer, and triethoxysilylethyl polydimethyl siloxyethylhexyl dimethicone.

Each of the coating materials is used in an amount of 1-5 wt% based on the total weight of the composition according to the formulation thereof. Polysiloxane has been widely used to treat the surface of metal oxide and inorganic material. Polysiloxane has a very low surface tension, and treatment therewith imparts excellent hydrophobicity and lubricity to the substrate. It has excellent water repellency and has no surface activity, and thus is widely used as a surface-treating agent. Silane is a surface-treating agent having a very good reactivity, because the Si-O bond thereof readily reacts with water to form silanol. It is lipophilic, is readily dispersed in esters, mineral oils and silicone fluids, and has good water repellency. An acrylate-silicone copolymer has increased compatibility with oils and esters due to the addition of acrylate, compared to silicone. It has excellent adhesion to the skin, shows long-lasting effects caused by high water repellency and forms an elastic, non- sticky film. [Advantageous Effects]

As described above, according to the present invention, the glossiness, properties-in-use and the like of inorganic particles can be controlled by etching the surface of the inorganic particles using a high energy source and a suitable concentration of acid. Also, the oil absorption, whiteness and water repellency of the etched organic particles can be improved by modifying the surface thereof. In addition, the glossiness of synthetic mica can be eliminated, and the oil absorption thereof can be improved, by forming structures on the surface of the synthetic mica using a controlled concentration of acid in controlled reaction conditions.

[Description of Drawings] FIG. 1 shows measurement results for the reflectivity of Example 2 of the present invention, measured using a goniophotometer .

FIG. 2 shows SEM (scanning electron microscope) photographs at 250Ox (a) and 2000Ox (b) of Example 2 of the present invention.

FIG. 3 shows two-dimensional and three-dimensional atomic force microscope images, which illustrate surface roughness caused by etching.

FIG. 4 is a schematic diagram of a bright face surface by soft-focus effects.

FIGS. 5 to 7 are goniophotometric reflection photographs taken at incident angles of 15 ^° , 45 and 75 ^° .

FIG. 8 is a SEM photograph of the surface structures of synthetic mica according to Example 9 of the present invention.

FIG. 9 is a SEM photograph of the surface of synthetic mica according to Comparative Example 6.

FIG. 9 is a SEM photograph of the surface of synthetic mica according to Comparative Example 7. [Mode for Invention]

Hereinafter, the present invention will be described in further detail with reference to examples and comparative examples, but the scope of the present invention is not limited only to these examples. The degree of etching is influenced by the concentration of acid, time, the amount of energy and the concentration of slurry, and thus the surface of inorganic particles becomes a shape like the moon's surface while the surface area of the inorganic particles increase. The structures on the surface and the roughness of the surface were observed with a scanning electron microscope (SEM) or an atomic force microscope, and the oil absorption of the inorganic particles was determined by measuring oil absorption per gram using an artificial sebum composition. Also, the coating content caused by surface modification was measured through volatile solids content.

Example 1: Etching of natural mica (muscovite; KAIs(AlSi₃O₁₀) (OH)₂) by acid treatment

90 wt% of hydrofluoric acid (HF) solution was added to a slurry reactor, and then 10 wt% of a natural mica fine particle solution was added thereto little by little, such that it did not come in contact with the reactor wall. Then, for complete wetting, the mixture solution was mechanically stirred for 30 minutes. Herein, the concentration of the hydrofluoric acid used in the acid treatment was 2-4 wt%. At this acid concentration, 10 wt% of a slurry was prepared, and microwave energy was applied to the slurry. Herein, the amount of energy was 660 W. The inorganic particles treated under such conditions were washed, filtered, dried and then crushed.

Example 2: Etching of synthetic mica (fluoro- phlogopite; KAl₂ (AlSi₃Oi₀) (F₂) by acid treatment

The same procedure as described in Example 1 was repeated, except that synthetic mica was used as inorganic particles .

Example 3: Etching of sericite (KAl₂ (AlSi₃Oio) (OH) ₂) by acid treatment

The same procedure as described in Example 1 was repeated, except that sericite was used as inorganic particles. The sericite is substantially the same as muscovite, but it has a low potassium (K⁺) content and a high water (H₂O) content, compared to muscovite.

Example 4: Etching of talc (Mg₃Si₄O₁₀) (OH)₂) by acid treatment

The same procedure as described in Example 1 was repeated, except that talc was used as inorganic particles.

Comparative Example 1: Use of insufficient amount of energy in acid treatment of synthetic mica

The same procedure as described in Example 2 was repeated, except that the amount of microwave energy was 150 W. In the process of applying high energy after acid treatment, a very small amount of etching occurred.

Comparative Example 2 : Use of excessive amount of energy in acid treatment of synthetic mica

The same procedure as described in Example 2 was repeated, except that the amount of microwave energy was

1200 W. In the process of applying high energy after acid treatment, overetching caused by the increase in energy occurred.

Comparative Example 3 : Treatment of synthetic mica with excessive concentration of acid

The same procedure as described in Example 2 was repeated, except that the concentration of hydrofluoric acid used in acid treatment was 25 wt%. It could be observed that the overetching of flake-like particles occurred, so that the original shape of the flake-like particles was broken.

Test Example 1 : Measurement of glossiness Glossiness after etching by acid treatment was compared between Examples 1-4 and Comparative Examples 1-2. For the measurement of glossiness, a goniophotometer (GP- 200, Murakami Color Lab.) and a glassmeter (Micro-TRI-Gloss, BYK Gardner) were used. The goniophotometer can provide reflectivity data by measuring reflectivity at 1° -angle intervals for an incident angle of 45° while rotating an angle range of -90° to 90^° after applying measurement powder to artificial leather. Also, the scattering pattern of light by etching can be identified by one-dimensional and two-dimensional graphs. In FIG. 1, (a) is a two-dimensional graph, (b) is a one-dimensional graph, a blue line is glossiness before etching, and a white line is glossiness after etching.

Also, the glossmeter can set incident angle and provide numerical values incident at three angles (20°, 60° and 85^°) . It can provide only fragmentary information compared to the goniophotometer, but it has an advantage in that it can measure a large amount of samples for a short time .

Table 1

The results in FIG. 1 are goniophotometric data for Example 1 before and after etching and show reflectivity values for an incident angle of 45°. From FIG. 1, it could be seen that the specular reflectivity for incident angle was reduced, and the diffuse reflectivity in the direction of incident angle was increased.

Also, from the results in FIG. 1, it could be seen that the glossiness of the inorganic particles was reduced through surface etching, such that they would be suitable for use in cosmetic applications. In addition, in the case of a very small amount of etching as in Comparative Example 1, glossiness was too high, and in the case of overetching as in Comparative Example 2, the specular reflection of powder was lost .

Test Example 2: Test of properties-in-use

The properties-in-use of inorganic particles were measured in terms of two factors, adhesion and spreadability . These two factors were measured using a rheometer. Spreadability was first measured as the friction force (gl) between rubber and a coated film. Adhesion was expressed as Δ(gl-g2)/gl x 100, wherein g2 is a value obtained in a second measurement after the first measurement. A lower measurement value (gl) of spreadability and a lower measurement value (Δ(gl-g2)/gl x 100) are significant values. The measurement results are shown in Table 2 below.

Table 2

From the results in Table 2, it could be seen that adhesion was increased due to etching, while spreadability maintained the value before etching. This suggests that the properties-in-use of powder after etching were similar to those after etching.

Test Example 3 : Measurement with SEM (scanning electron microscope)

In order to examine the size of the inorganic particles of Example 2 and the etching tendency of the surface of the inorganic particles, the inorganic particles were measured with SEM (scanning electron microscope) . SEM

(S-4300, Hitachi) was used at two magnifications of 250Ox and 2000Ox. The 250Ox magnification (FIG. 2 (a) ) was used to observe the size of the inorganic powder and the presence or absence of cracking, and the 2000Ox magnification (FIG. 2 (b) ) was used to observe the etching tendency of the inorganic particle surface. The observation results are shown in FIG. 2.

From the results of FIG. 2, it could be seen that the smooth surface of the inorganic particles was etched to a thickness of 50-200 nm, and the primary particles themselves were not damaged by etching.

Example 5: Surface modification of natural mica KAI2 (AlSi_3_Oio) (OH)₂) etched by acid treatment, with coating material The surface modification of the inorganic particles prepared in Example 1 was performed by coating the inorganic particles with a coating material.

Example 6: Surface modification of synthetic mica (KAl₂(AlSi₃Oi_O)F₂) etched by acid treatment, with coating material

The surface modification of the inorganic particles prepared in Example 2 was performed by coating the inorganic particles with a coating material.

Example 7: Surface modification of sericite KAl₂ (AlSi₃Oio) (OH)₂) etched by acid treatment, with coating material

The surface modification of the inorganic particles prepared in Example 3 was performed by coating the inorganic particles with a coating material.

Example 8: Surface modification of synthetic mica (Mg₃Si₄Oi₀) (OH)₂) etched by acid treatment, with coating material

The surface modification of the inorganic particles prepared in Example 4 was performed by coating the inorganic particles with a coating material.

Comparative Example 4: Use of insufficient amount of energy in acid treatment of synthetic mica

The same procedure as described in Example 6 was repeated, except that the amount of microwave energy was 150 W. In the process of applying high energy after acid treatment, a very small amount of etching occurred due to a reduction in energy. The synthetic mica thus treated could be used as an inorganic powder raw material, but the properties thereof were close to those of the parent powder.

Comparative Example 5: Use of excessive amount of energy in acid treatment of synthetic mica

The same procedure as described in Example 6 was repeated, except that the amount of microwave energy was 1200 W. In the process of applying high energy after acid treatment, overetching caused by the increase in energy occurred.

Test Example 4 : Measurement of oil absorption The oil absorption of Examples 5-8 and Comparative Examples 4-5 before coating was compared with the oil absorption after coating. For this purpose, caprylic/capric triglyceride (Neobee M-5) was added dropwise to 1 g of powder provided in each of Examples 5-8 and Comparative Examples 4-5, and the amount (g) of triglyceride absorbed in the powder was measured. The measurement results are shown in Table 3 below. Table 3 : Measurement of oil absorption

As can be seen in Table 3, the oil absorption before coating was increased to about 110-250% after coating. Comparative Example 5 showed an increase in oil absorption due to an increase in the specific surface area thereof in a state in which the parent powder thereof was completely decomposed due to overetching, but it was not useful as a cosmetic raw material due to a rough touch caused by overetching .

Test Example 5 : Measurement of roughness with atomic force microscope

The roughness of surface features caused by coating was measured with an atomic force microscope (see FIG. 3) .

The roughness was determined by converting surface features into numerical values and averaging the numerical values.

Higher numerical values show that the surface was etched deeper. The measurement results of roughness are shown in Table 4 below.

Table 4 : Comparison of roughness between before coating and after coating

Test Example 6 : Colorimetric measurement

Changes in the color of Example 5 between before coating and after coating were measured with a colorimeter.

The changes in color were expressed as L* for luminosity and a* and b* for saturation. The measurement results are shown in Table 5 below. Table 5

Before coating After coating

L* (luminosity) 85 90 a* (red-green) 0.20 0.39 b* (yellow-blue) 1.99 1.95 As can be seen in Table 5, the luminosity of Example

5 before coating was increased after coating. a* value for saturation was increased, suggesting that it was shifted to red. Because of the characteristics of white pigments, the saturation value was significant in a narrow range.

Test Example 7: Comparison of water repellency Water repellency of Examples 5-8 and Comparative Examples 4-5 was compared between before coating and after coating. The measurement of water repellency was performed to examine the wettability of inorganic powder itself in water upon the use of products and to improve the inorganic powder.

Water repellency was measured using contact angle in the following manner.

Contact angle is a measure indicative of a solid surface and is mostly measured by a water drop. A lower contact angle indicates a higher wettability (hydrophilicity) and a higher surface energy, and a higher contact angle indicates a lower wettability

(hydrophobicity) and a lower surface energy. The contact angle of a liquid on a flat solid surface is measured at the contact point between the solid surface and the end point of the water drop curve at the liquid-solid-gas interface .

To measure the contact angle, the solid surface must be flat. Then, water is dropped on the solid surface. The diameter of the water drop should generally be a few mm. A double-sided adhesive film having excellent shear adhesion is fixed to a slide glass, and each of the surface-modified samples is plated on the slide glass and measured for contact angle. The measurement results of water repellency are shown in Table 6 below.

Table 6 : Measurement results of water repellency

As can be seen in Table 6, the coated powders all showed significantly increased water repellency compared to the uncoated powders.

Example 9: Formation of structures on synthetic mica (KAl₂ (AlSi_jOio) F₂) by acid treatment

50 g of synthetic mica (KAl₂(AlSi₃OiO)F₂) and 450 g of hydrofluoric acid were placed in a slurry reactor little by little such that they did not come in contact with the reactor wall. Then, for completing wetting, the mixture was mechanically stirred for 30 minutes, and the concentration of the hydrofluoric acid as a solvent was 4 wt%. At this acid concentration, 10 wt% of a slurry was prepared and was applied with microwave energy, ultrasonic energy, plasma energy or heating. Herein, the amount of energy used was 900 J/ml , and the slurry was aged at a temperature of room temperature to 50 ^°C for 1 hour to perform a crystallization step for forming surface structures . The inorganic powder treated in such conditions was washed, filtered, dried and then crushed. In such conditions, surface structures, including rod- shaped and cross-shaped surface structures, were formed on the surface of the synthetic mica, and yield was 90%.

Comparative Example 6: Use of insufficient amount of energy in acid treatment of synthetic mica

Surface structures were formed in the same manner as described in Example 9 was repeated, except that the amount of microwave energy was 200 J/ml .

Comparative Example 7: Use of excessive amount of energy in acid treatment of synthetic mica Surface structures were formed in the same manner as described in Example 9 was repeated, except that the amount of microwave energy was 1300 J/ml.

Test Example 8 : Measurement of glossiness with goniophotometer

The glossiness at various angles of the powders prepared in Example 9 and Comparative Examples 6-7 was compared between before and after formation of the surface structures. For this purpose, the glossiness of the powders was measured with a goniophotometer (GP-200, Murakami Color Lab.) .

The goniophotometer can provide reflectivity data by measuring reflectivity at 1° -angle intervals for an incident angle of 45^° while rotating an angle range of -90° to 90° after applying measurement powder to artificial leather. Through such data, it is possible to expect the glossiness of the powder applied on a rough face (see FIG. 4) . FIGS. 5 to 7 are goniophotometric data for powder before and after forming surface structures in Example 9 and are two-dimensional graphs showing reflection for incident angles of 15°, 45 "and 75°. As can be seen in FIGS. 5 to 7, specular reflectivity for incident angle was decreased and diffuse reflectivity in the direction of incident angle and all directions was increased.

Thus, it can be seen that, when the powder of Example 9 according to the present invention is applied in a cosmetic raw material, it will reduce specular glossiness caused by light on a face, reduce the difference between light and shade, and can be applied as a powder raw material which can make the skin looking beautiful.

Test Example 9 : Measurement of oil absorption The oil absorption of the powder prepared in each of Example 9 and Comparative Examples 6-7 was compared between before and after etching by acid treatment . For this purpose, caprylic/capric triglyceride (Neobee M-5) was added dropwise to 1 g of the powder, and the amount (g) of triglyceride absorbed in the powder was measured. The powder was placed on a Petri dish, the triglyceride was added dropwise thereto, and the mixture was uniformly spread with a spatula. The addition of the triglyceride oil was continued until it was not absorbed in the powder, and the amount of oil added was averaged.

Table 7 : Measurement of oil absorption

As can be seen in Table 7, the oil absorption before treatment was increased after treatment to 110%-200% depending on the degree of etching. Comparative Example 7 showed an increase in oil absorption due to an increase in the specific surface area thereof in a state in which the parent powder thereof was completely decomposed due to overetching, but it was not useful as a cosmetic raw material .

Test Example 10: Measurement with SEM (scanning electron microscope) To confirm the formation of structures on the surface of synthetic mica, SEM (S-4300, Hitachi) at 2000Ox magnification was used to observe the powders of Example 9 of the present invention and Comparative Examples 6-7. The observation results are shown in FIGS. 8 to 10. As can be seen in FIGS. 8 to 10, in the powder of Comparative Example 6, a very small amount of structures were formed due to a decrease in energy during the process of applying high energy after acid treatment, and the produced powder would be used as an inorganic power raw material, but the properties thereof were close to those of the parent powder. In the case of Comparative Example 7, the over-growth of the surface structures occurred due to an increase in energy in the process of applying high energy after acid treatment, and this over-growth of surface structures led to a decrease in the utility of the powder product. However, it could be observed that rod- shaped structures were formed on the surface of the synthetic mica of Example 9, and L-shaped, star-shaped, cross-shaped and octahedral -shaped structures were also present on the surface.

[industrial Applicability]

As described above, the present invention provides the method of etching inorganic particles using a high- energy source and a suitable concentration of acid in controlled reaction conditions. Also, it provides the method for forming structures on the surface of synthetic mica. Moreover, it provides the method for modifying the surface of the inorganic particles etched according to said etching method, with a coating material. When inorganic particles are treated according to the method provided in the present invention, the glossiness of the inorganic particles themselves can be reduced, the properties-in-use thereof can be improved, and thus the treated inorganic particles will be more suitable for use as cosmetic raw materials .

Claims

[CLAIMS]

[Claim l]

A method of modifying the surface of inorganic particles by acid treatment using a high-energy source, the method comprising the steps of:

(1) adding inorganic particles to an acid and stirring the mixture to prepare a slurry; and

(2) applying a high—energy source to the slurry, and then washing, filtering, drying and then crushing the inorganic particles. [Claim 2]

The method of Claim 1, wherein the acid in the step (1) is at least one selected from the group consisting of hydrofluoric acid, nitric acid, acetic acid, hydrochloric acid and phosphoric acid. [Claim 3]

The method of Claim 1, wherein the acid is used at a concentration of 1-20 wt%.

[Claim 4] The method of Claim 1, wherein the high-energy source in the step (2) is at least one selected from the group consisting of microwave energy, ultrasonic energy, plasma and heating.

[Claim 5] The method of Claim 1, wherein the high-energy source is used in an energy amount of 200-1000 W. [Claim 6]

The method of any one of Claims 1 to 5, which additionally comprises, after the step (2) , (3) a step of coating the crushed inorganic particles with a coating material . [Claim 7] The method of Claim 6, wherein the coating material in the step (3) is at least one selected from the group consisting of dimethicone, methicone, triethoxy caprylylsilane, acrylate/tridecyl/triethoxysilylpropyl methacrylate/dimethicone methacrylate copolymer, and triethoxysilylethyl polydimethyl siloxyethylhexyl dimethicone . [Claim 8]

A method for forming structures on the surface of synthetic mica, the method comprising the steps of: (1) treating the surface of synthetic mica with an acid; and

(2) aging the acid-treated synthetic mica at a temperature of 30-40 ^°C for 30 minutes to 2 hours to form structures on the surface of the synthetic mica. [Claim 9]

The method of Claim 8, wherein the amount of energy, which is applied when the surface of the synthetic mica is treated with the acid, is in a range of 500-1000 j/ml .

[Claim lθ] The method of Claim 8, wherein the acid in the step (1) is at least one selected from the group consisting of hydrofluoric acid, nitric acid, acetic acid, hydrochloric acid and phosphoric acid. [Claim ll] The method of Claim 8, wherein the acid is used at a concentration of 2-6 wt%. [Claim 12]

The method of any one of Claims 8 to 11, which additionally comprises, after the step (2), (3) a step of wet-coating, dry-coating or vapor-coating the synthetic mica surface having the structures formed thereon, with a coating material at a temperature of 80-150 ^°C .

[Claim 13] The method of Claim 12, wherein the coating material in the step (3) is at least one selected from the group consisting of methicone, triethoxy caprylylsilane, acrylate/tridecyl/triethoxysilylpropyl methacrylate/dimethicone methacrylate copolymer, and triethoxysilylethyl polydimethyl siloxyethylhexyl dimethicone .