WO2005077329A1

WO2005077329A1 - Silver/polymer colloidal nanocomposites and a process for preparation of the same, and cosmetic compositions containing the same

Info

Publication number: WO2005077329A1
Application number: PCT/KR2005/000371
Authority: WO
Inventors: Jin Woong Kim; Jong Suk Lee; Su Jin Kim; Yong Jin Kim; Junoh Kim; Sang Hoon Han; Ih Seop Chang
Original assignee: Amorepacific Corporation
Priority date: 2004-02-11
Filing date: 2005-02-07
Publication date: 2005-08-25
Also published as: KR20050080805A

Abstract

The present invention relates to silver/polymer composite nanospheres and to a process for preparation thereof. More particularly, the present invention relates to silver/polymer composite nanospheres obtained by depositing silver nanoparticles on the surface of polymeric support and to a process for preparation thereof. Further, the silver/polymer composite nanospheres according to the present invention may not cause general discoloration and cohesion by colloidal silver and thereby can be used as a preservative having strong antimicrobial activity. In addition, the silver/polymer composite nanospheres according to the present invention can preserve cosmetics during a long period, not using conventional preservatives. Accordingly, the present invention relates to silver/polymer composite nanospheres to be used as a cosmetic preservative and to cosmetic compositions containing the same.

Description

Silver/polymer colloidal nanocomposites and a process for preparation of the same, and cosmetic compositions containing the same

BACKGROUD OF THE INVENTION

1. Field of the Invention The present invention relates to silver/polymer composite nanospheres and to a process for preparation thereof. More particularly, the present invention relates to silver/polymer composite nanospheres obtained by depositing silver nanoparticles on the surface of polymeric support and to a process for preparation thereof. Further, the present invention relates to silver/polymer composite nanospheres to be used as a cosmetic preservative and to cosmetic compositions containing the same.

2. Description of Prior Art In general, cosmetics are easily contaminated by bacteria, fungi, etc. So, chemical preservatives such as paraben, imidazohdinyl urea, phenoxyethanol, etc. have been used in order to prevent such contamination. However they may cause skin irritation or allergy limiting the contents that can be used. Therefore, there was a need to develop a novel preservative system having higher preservative activity than chemical preservatives and excellent dermal safety. Nageli and Christian reported, in Denkschr. Schweiz, Naturforsch Ges., 1894, that metals such as mercury, silver, copper, cadmium, chromium, nickel, lead, cobalt, zinc, etc. exhibit bactericidal activity in the colloidal phase. However, most of said metal particles are classified into heavy metals, and therefore it is substantially impossible to incorporate them into cosmetic compositions. Nevertheless, silver is harmless and exhibits sufficiently strong bactericidal activity in the colloidal phase to be applied as a cosmetic. Accordingly, many efforts to introduce these characteristics of silver into a cosmetic have been made. Ultra-fine silver exhibits increasingly strong antimicrobial activity as its diameter becomes smaller. Recently, most ultra-fine silver has been prepared in nano-scale by chemical reduction, electrolysis, etc. Korean Patent Application Nos. 2002-009158, 2002-0002505 and 2001-0024439 describe methods for preparing silver nanoparticles by chemical reduction. In addition, US Patent No. 5,932,251 describes a method for preparing silver nanoparticles by electrolysis and the application thereof as a cosmetic. The above patents accomplished the preparation of silver nanoparticles and described various applications thereof using the antimicrobial effects of silver. However, although the silver nanoparticles prepared by said methods can exhibit excellent antimicrobial effects in conventional cosmetic compositions, they may ultimately become discolored by reducing agents added to the composition, and it is therefore substantially impossible to apply them as cosmetics. In order to improve said defects, US Patent No. 6,030,627 discloses an approach to induce the expression of silver activity by intercalating ultra- fine silver inside the lattice structure of inert support. However, this approach lowers silver activity rapidly and thereby should intercalate excessive silver. Further, it has the same problem of ultimately being discolored in a cosmetic formulation, as silver nanoparticles. The reason that cosmetic compositions containing silver have excellent antimicrobial activity, but cannot ensure the stability of the formulations, is related to the behavior, in a formulation, of the dissociated silver ions, which exert antimicrobial activity. In detail, silver ions are successively reduced by reducing agents (surfactants, polyols, chelating agents, etc.) contained in cosmetic compositions, to form hetero-particles of silver. However the absorbance behavior of the silver hetero-particles formed shifts the characteristic absorbance band, and thereby the color seems to be discolored on observation with the naked eye. Therefore, in order to ultimately incorporate silver nanoparticles into cosmetic compositions, dissociation into silver ions should be performed effectively and, at the same time, the silver hetero-particles formed incidentally should be selectively blocked off.

SUMMARY OF THE INVENTION Under this circumstance, the present inventors have conducted extensive studies in order to develop a silver system for maintaining the antimicrobial activity of ultra-fine silver and for preventing discoloration by reducing agents. As a result thereof, it was found that the composite nanospheres obtained by depositing silver nanoparticles (hereinafter, "Ag nanoparticles") on the wide surface of porous polymer can exhibit excellent antimicrobial activity in a cosmetic composition as well as blocking silver ions within the composition from discoloration by reducing agents. This provides the possibility of developing cosmetics to be preserved for a long time. Thus, the present invention was completed. Therefore, one object of the present invention is to provide silver/polymer composite nanoparticles (hereinafter, "silver/polymer nanocomposites") obtained by uniformly depositing Ag nanoparticles on the surface of polymeric support, and a process for preparation thereof. Another object of the present invention is to provide silver/polymer nanocomposites as a cosmetic preservative, and cosmetic compositions containing the same.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the scanning electron microscopy images showing the surface (a) and the inside (b) of the porous polymer particles prepared in Example 2. Figure 2 shows the transmission electron microscopy images of silver/polymer nanocomposites: (a) image is of the nonporous silver/polymer nanocomposites prepared in Comparative Example 2; and (b) image is of the porous silver/polymer nanocomposites prepared in Example 2. Figure 3 shows the X-ray diffraction patterns of silver/polymer nanocomposites: (a) pattern is of polymer particles; (b) pattern is of the nonporous non-functional silver/polymer nanocomposites prepared in Comparative Example 1 ; (c) pattern is of the nonporous functional silver/polymer nanocomposites prepared in Comparative Example 2; (d) pattern is of the porous non-functional silver/polymer nanocomposites prepared in Example 1 ; and (e) pattern is of the porous functional silver/polymer nanocomposites prepared in Example 2. Figure 4 shows the ultraviolet spectra of the cosmetics containing colloidal silver and silver/polymer nanocomposites. (a) ultraviolet spectrum is of the cosmetic of Comparative Formulation 7 containing colloidal silver, directly after the preparation thereof; (b) ultraviolet spectrum is of the cosmetic of Comparative Formulation 7 containing colloidal silver, after 6-month storage at 40 ^°C ; (c) ultraviolet spectrum is of the cosmetic of Fomiulation 6 containing porous silver/polymer nanocomposites, directly after the preparation thereof; and (d) ultraviolet spectrum is of the cosmetic of Formulation 6 containing porous silver/polymer nanocomposites, after 6-month storage at 40 ^°C .

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to silver/polymer nanocomposites obtained by uniformly depositing Ag nanoparticles on the surface of polymeric support. The silver/polymer nanocomposites provided by the present invention may be obtained by depositing Ag nanoparticles on the wide surface of porous particles produced by suspension polymerization, and the process for preparation thereof may comprise the following steps of (1) dissolving monomer, crosslinking agent and initiator in a solvent to give a monomer solution; (2) emulsifying said monomer solution in the presence of dispersion stabilizer to give an emulsion; (3) polymerizing said emulsion and then removing the solvent to collect porous polymer particles; and (4) depositing Ag nanoparticles, formed by reducing silver salts with a reducing agent, on the surface of the porous polymer particles collected in step (3). In the present invention, porous polymer particles with large surface area can be obtained by suspension polymerization. In brief, monomer/crosslinking agent/initiator are dissolved in a solvent, and then emulsified with a homogenizer, in the presence of dispersion stabilizer. The obtained emulsion is then subjected to suspension polymerization under stirring at a polymerization temperature. Porous structure can be obtained by inducing phase separation of the crosslinked polymer network during suspension polymerization. In the case of polymerization reaction within a liquid droplet containing monomer, crosslinking agent, initiator and solvent, the polymer network may lose solubility to the solvent as it propagates, thereby forming nano-scale spherical aggregates. Because such fine spheres formed within a liquid droplet have a strong hardened property, solvent may fill up between the aggregates. Thus, porous polymer particles with maximized surface area can be obtained by selectively removing the solvent. At this time, copolymerization of monomer having hydroxy group, amine group, nitrile group and the like can produce porous polymer particles having mutual functional groups to more effectively induce the deposition of Ag nanoparticles on the surface thereof. Nano-scale deposition of Ag nanoparticles is performed by the reduction of silver salts. In detail, porous polymer is dispersed in distilled water, and thereto is added an aqueous solution of silver salts, which then is reduced into Ag nanoparticles by a reducing agent. After filtration and drying processes, porous polymer composite spheres with Ag nanoparticles deposited are obtained. The composite spheres, with Ag nanoparticles uniformly deposited on the surface of porous polymer particles, can be incorporated into various cosmetic compositions. An Ag nanoparticle to be deposited on said porous polymer may be obtained by reducing one or more silver salts selected from the group consisting of silver acetate, silver bromide, silver carbonate, silver chloride, silver citrate, silver cyanide, silver fluoride, silver iodide, silver nitrate, silver nitrite, silver phosphate, silver sulfate and silver sulfide. It may be preferable to use Ag nanoparticles obtained by reducing silver nitrate. In the preparation of the present silver/polymer nanocomposites, the content of Ag nanoparticles to be deposited may be preferable in a range of 0.001 to 30% by weight based on the total weight of polymer. In addition, the particle size of Ag nanoparticles may be preferable in a range of 1 to 50 nm. In step (1), a monomer used for porous polymer particles may, if it is capable of radical polymerization, not be limited to aspecific kind. Further, porous polymer may be prepared by copolymerization of monomer and crosslinking agent or by using only crosslinking agent. A monomer may be selected from the group consisting of styrene; acrylate; vinyl acetate; vinyl ether; unsaturated carboxylic acid including maleic acid; alkyl(meth)acrylamide; (meth)acrylonitrile; and their derivatives. Specifically, the monomer may be styrene, p- or 77z-methylstyrene, p- or -ethylstyrene, p- or m-chlorostyrene, p- or -chloromethylstyrene, styrenesulfonic acid, p- or -t-butoxystyrene, methyl(meth) acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth) acrylate, isobutyl(meth) acrylate, t-butyl(meth)acrylate,

2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, glycidyl(meth)acrylate, dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl ether, allylbutyl ether, allylglycidyl ether, unsaturated carboxylic acid including (meth)arylic acid and maleic acid, alkyl(meth)acrylamide or (meth)acrylonitrile. Further, a crosslinking agent used in said step (1) may be capable of radical polymerization and be selected from the group consisting of allyl compounds including divinylbenzene and diallylphthalate; (poly)alkylene glycol di(meth)acrylate including (poly)ethylene glycol di(meth)acrylate; urethane acrylate; epoxy acrylate; and their derivatives. Specifically, it may be allyl compounds including divinylbenzene, 1,4-divinyloxybutane, divinylsulfone, diallylphthalate, diallylacrylamide, triallyl(iso)cyanurate and triallyltrimellitate; (pόly)alkylene glycol di(meth)acrylate including (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth) acrylate, pentaerythritol tetra(meth) acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerytliritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate and glycerol tri(meth)acrylate; urethane acrylate; or epoxy acrylate. The content of said crosslinking agent may determine the porosity of final polymer particles. In general, it may be preferable in a range of 30% or more by weight based on the total weight of monomer. If the content is less than 30%, phase separation may be weakened and thereby porosity and surface area may be decreased. Further, an initiator used in the present invention may be an oil-soluble initiator and selected from the group consisting of peroxides including benzoyl peroxide; azo compounds including 2,2-azobisisobutyronitrile; and their derivatives. Specifically, it may be peroxides including benzoyl peroxide, lauryl peroxide, ochlorobenzoyl peroxide, o-methoxybenzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, 1 , 1 ,3 ,3 -tetramethylbutylperoxy-2-ethylhexanoate, dioctanoyl peroxide and didecanoyl peroxide; or azo compounds including 2,2-azobisisobutyronitrile, 2,2-azobis(2-methylbutyronitrile) and

2,2-azobis(2,4-dimethylvaleronitrile). The amount of initiator to be used may be preferable in a range of 0.1 to 3% by weight based on the total weight of monomer. A solvent used in said step (1) may have the same solubility parameter as that of monomer and be selected from the group consisting of linear alkanes such as hexane; alcohols having from 4 to 10 carbon atoms such as butanol; alkyl esters having 7 or more carbon atoms such as n-hexyl acetate; aliphatic ketones; aromatic hydrocarbons such as toluene; chlorine compounds such as methylene chloride; and their derivatives. Specifically, it may be, but not limited hereto, linear alkanes such as hexane, heptane, octane, nonane and decane; alcohols having from 4 to 10 carbon atoms such as butanol, linear or branched pentanol, hexanol, heptanol, octanol, nonanol and decanol; alkyl esters having 7 or more carbon atoms such as n-hexyl acetate, 2-ethylhexyl acetate, methyl oleate, dibutyl sebacate, dibutyl adipate and dibutyl carbamate; aliphatic ketones such as methylisobutyl ketone and isobutyl ketone; aromatic hydrocarbons such as benzene, toluene and o- or 7-xylene; chlorine compounds such as methylene chloride, or chloroform and carbon tetrachloride. It may be preferable to use toluene or ketone in consideration of phase separation for forming porous structure. A dispersion stabilizer used in said step (2) may be a water-soluble polymer and specifically gelatin, starch, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alkyl ether, polyvinyl alcohol or polydimethyl siloxane/polystyrene block copolymer. The amount thereof may be adequate so long as it may prevent sedimentation or cohesion of polymer particles produced in the emulsification process; and is preferable in a range of 0.1 to 30% by weight based on the total weight of reactant. If the amount is less than 0.1%, dispersion stability may be rapidly decreased by interfacial deposition. On the other hand, if the amount is more than 30%, the viscosity of thedispersion system may suddenly increase, making the processes impossible to control. The porous polymer particles obtained may have a spherical structure with an average particle size of 1~100 μm, ranging from 0.01 μm to 1,000 μm of particle size. Further, they may have 10 m²/g or larger surface area with small pores of 1~10 nm and thereby can be very effective in deposition of Ag nanoparticles. In d step (4), the deposition of Ag nanoparticles is performed in aqueous phase. In detail, porous polymer is dispersed in distilled water and silver salt is dissolved therein. Thereto, a reducing agent is added in a concentration of approximately 0.0001 to 1%, to reduce the silver salt into Ag nanoparticles, which are simultaneously deposited on the porous polymer particles. A reducing agent to be used in the step may be hydrazine, LiAlBH₄, NaBH₄, ethylene oxide and its derivatives, etc. If the concentration is less than 0.0001 %, the reduction of silver salts may not be performed effectively. On the other hand, if the concentration is more than 1%, the reduction may be performed too rapidly, making uniform deposition difficult. The silver/polymer nanocomposites provided by the above method are fine spherical powder consisting of nano-scale silver particles deposited on the surface of porous polymer particles, and thereby can be easily dispersed and combined in a cosmetic base, so as to be applicable in various formulations. Further, the present invention relates to silver/polymer nanocomposites to be used as a cosmetic preservative and to cosmetic compositions containing the same. In the cosmetic composition of the present invention, said silver/polymer nanocomposites, as a cosmetic preservative, may be incorporated in an amount of 0.01 to 5% by weight based on the total weight of the cosmetic composition. In case of the cosmetic composition containing the silver/polymer nanocomposites of the present invention, its formulation is not limited to specific kind. Specifically, it may be formulated into skin softeners, nutrient toilet waters, massage creams, nutrient creams, gels, packs, essences, lipsticks, make-up bases, foundations, lotions, ointments, creams, patches, aerosols, sprays, powders, eye shadows or body cleansers.

PREFERRED EMBODIMENT OF THE INVENTION The present invention will be described in more detail by way of the following examples, comparative examples and experimental examples. However, these examples are provided for the purpose of illustration only and should not be construed as limiting the scope of the invention, which will be apparent to one skilled in the art.

<Comparative Example 1> Preparation of nonporous non-functional polymer particles and deposition of Ag nanoparticles thereon Nonporous non-functional polymer particles were prepared in the following process. Methylmethacrylate/ethylene glycol dimethacrylate (as a crosslinking agent) were mixed in a weight ratio of 30/70 in a reactor, to give lOOg of solution. As an initiator, 2,2-azobis(2,4-dimethylvaleronitrile) of lwt% based on the weight of monomer was added to said solution and completely dissolved under stimng at room temperature. The obtained solution was then added to 1% aqueous solution of polyvinyl alcohol (with 89% average saponification value), and emulsified at 6,000rpm by a homogenizer for 5 minutes. At this time, the concentration of methylmethacrylate/crosslinking agent/initiator solution in aqueous phase was 15wt%. Subsequently, the reactor was heated to 70 ^°C and polymerization was performed for 10 hours. The resulting mixture was then passed through filter paper to collect the nonporous polymer particles. The collected product was repeatedly washed with methanol to remove residue reactant and dispersion stabilizer, and then dried in a vacuum oven for 24 hours, to give 92g of polymer particles as powders. lOg of the polymer particles obtained were dispersed in sufficient water containing

0.5 wt% of Tween 80 to give a concentration of 10wt% based on the total weight.

Further, silver nitrate of 3.5wt% based on the total weight was dissolved to give aqueous solution, which was then added to the polymer dispersion. Next, hydrazine of

0.1 wt% based on the total weight was slowly added thereto. After reaction for 6 hours, the resulting mixture was passed through filter paper and then dried in a vacuum oven for 24 hours, to give 9.5g of polymer particles with Ag nanoparticles deposited thereon as powders.

<Comparative Example 2> Preparation of nonporous polymer particles having hydroxy group and deposition of Ag nanoparticles thereon Polymerization was performed by the same procedure as described in Comparative

Example 1, using methylmethacrylate/vinyl acetate/ethylene glycol dimethacrylate in a weight ratio of 24/6/70. After the termination of polymerization, 0.8wt% of sodium hydroxide was added to the reaction mixture and then acetate was saponificated at room temperature for 10 hours, to give nonporous polymer particles having hydroxy group thereon. The deposition of Ag nanoparticles was performed by the same procedure as described in Comparative Example 1.

<Comparative Example 3> Preparation of Ag nanoparticles In order to compare the efficacy of silver/polymer nanocomposites, Ag nanoparticles were prepared. Firstly, silver nitrate of 3.5wt% based on the total weight was dissolved in water containing 0.5 wt% of Tween 80 to give aqueous solution. Hereto was slowly added hydrazine of 0.1 wt% based on the total weight. After reaction for 6 hours, the resulting mixture was repeatedly centrifuged to collect Ag nanoparticles, which were formed into dispersions having a content of 3400ppm.

<Example 1> Preparation of porous non-functional polvmer particles and deposition of Ag nanoparticles thereon Polymerization was perforaied by the same procedure as described in Comparative Example 1, using methylmethacrylate/ethylene glycol dimethacrylate/toluene in a weight ratio of 18/42/40, to give 56g of porous polymer particles. The deposition of Ag nanoparticles was performed by the same procedure as described in Comparative Example 1.

<Example 2> Preparation of porous polvmer particles having hydroxy group and deposition of Ag nanoparticles thereon Polymerization was performed by the same procedure as described in Comparative Example 2, using methylmethacrylate/vinyl acetate/ethylene glycol dimethacrylate/toluene in a weight ratio of 12/6/42/40, to give 55g of porous polymer particles. The deposition of Ag nanoparticles was perforaied by the same procedure as described in Comparative Example 1. Experimental Example 1> Characterization of silver/polymer nanocomposites The silver/polymer nanocomposites prepared in Examples 1~2 and Comparative Examples 1-2 were characterized by BET (Brunauer, Emmett and Teller) techniques and Atomic Absorption (Spectro) Photometry. The results are shown in Table 1. [Table 1]

As shown in Table 1, the silver/polymer nanocomposites prepared in Comparative Examples 1 and 2, regardless of surface functional groups, had very small surface area and the content of silver deposited was very low. On the contrary, the porous polymer particles had 200 m7g or more surface area, regardless of surface functional groups. Further, the content of silver deposited increased by imparting surface porosity and surface functionality, hi conclusion, the results indicate that surface area is the most important factor in nano-scale deposition.

Experimental Example 2> Structural analysis of silver/polymer nanocomposites The silver/polymer nanocomposites prepared by conventional suspension polymerization in Comparative Examples 1 and 2 were known to have smooth surfaces. However, the porous polymer particles prepared in Examples 1 and 2 have strong pore-structures at the inside and on the surface thereof. The porous functional polymer particles prepared in Example 2 were observed for particle structures by scanning electron microscopy. The results are shown in Figure 1. Because the particles were prepared by suspension polymerization, they have polydispersity as a whole, but have strong porosity on the surface thereof. The transmission electron microscopy images of the silver/polymer nanocomposites obtained by the deposition of Ag nanoparticles are shown in Figure 2. In case of (a) using nonporous polymer particles, the deposition of Ag nanoparticles was done only on the surface. On the contrary, in case of (b) using porous polymer particles, Ag nanoparticles were distributed unifonnly on the surface and at the inside thereof, to be evaluated as successful deposition. In addition, the crystallinity of the Ag nanoparticles introduced was analyzed by X-ray diffraction and the results are shown in Figure 3. As shown in Figure 3, all the Ag nanoparticles deposited formed face-centered cubic crystal phase, to be verified as pure silver. In addition, the silver/polymer nanocomposites prepared in Example 2 showed the highest deposition efficiency and formed the strongest crystal phase. The above results confirmed that the silver/polymer nanocomposites prepared in Example 2 are the most appropriate. Particularly, the Ag nanoparticles inside the particles are expected to exhibit strong preservative activity, due to dissociation into silver ions through pores, together with the Ag nanoparticles on the surface of the particles.

<Formulations 1 and 2 and Comparative Formulations 1 and 2> Skin softeners (Skin lotions) In order to determine the preservative activity of the silver/polymer nanocomposites prepared in Comparative Examples 1 and 2 and Examples 1 and 2, depending on their surface characteristics, in a cosmetic composition, skin softeners were formulated in the compositions of Table 2. [Table 2]

<Test 1> Preservative Activity Test In order to evaluate the preservative activity, pooled bacterial suspension -Escherichia coli : ATCC 8739, Staphylococcus aureus : ATCC 6538, Pseudomonas aeruginosa : ATCC 99027- was mixed with 20~30g of the cosmetics of Formulations 1 and 2 and Comparative Formulations 1 and 2, to achieve an initial concentrations of 10⁶ cfu (colony forming unit)/g. These were cultured in an incubator at 30 to 32°C for 4 weeks and the colonies in lg of the cosmetics were counted every 7 days, i.e. at 1 day, 7 days, 14 days, 21 days and 28 days after inoculation. The results are shown in Table 3. In case of fungi, pooled mold suspension - Penicillium citrium : ATCC 9849 and Aspergillus niger : ATCC 16404 - was mixed with each test product, to achieve an initial concentration per test product of 10⁶ cfu (colony forming unit)/g. They were cultured in an incubator at 25 °C and damp smell, mold spawning and spore germination on the surface of test product were observed every 7 days. The results are shown in Table 3. [Table 3]

- : For 8 weeks, no damp smell, no spawning and no spore germination and good condition

4- : Within 4 weeks, fungi were observed on the wall or the cover of the container

++ : Within 4 weeks, damp smell and fungi were observed on part of the surface of the test product

+++ : Within 4 weeks, damp smell and fungi were observed on the whole surface of the test product As shown in Table 3, the preservative activity of the silver/polymer nanocomposites was increased by surface porosity and surface functionality thereof. As confirmed in Table 1, this is because the improved deposition efficiency may increase the content of silver. Thus, it was established that the surface area maximization and surface interaction sites in such a composite system play important parts in inducing the expression of silver preservative activity.

<Formulations 3 and 4 and Comparative Formulations 3~5> Skin softeners (Skin lotions) In order to determine the preservative activity of the silver/polymer nanocomposites prepared in Example 2, depending on its amount in a skin softener, skin softeners were formulated in the compositions of Table 4. For comparison, Comparative Formulation 4 containing the same content of Ag nanoparticles, prepared in Comparative Example 3, was formulated and its preservative activity was compared. Further, Comparative Formulation 5 containing a conventional chemical preservative, i.e. methylparaben was formulated. [Table 4]

<Test 2> Preservative Activity Test Preservative activity test was performed by the same procedure as described in Test 1, and the results are shown in Table 5.

[Table 5]

<Description of Grade> - : For 8 weeks, no damp smell, no spawning and no spore gennination and good condition

+ : Within 4 weeks, fungi were observed on the wall or the cover of the container

++ : Within 4 weeks, damp smell and fungi were observed on part of the surface of the test product +++ : Within 4 weeks, damp smell and fungi were observed on the whole surface of the test product

As shown in Table 5, the preservative activity of the silver/polymer nanocomposites was increased by increasing the amount thereof, and was similar to that of the Ag nanoparticles contained in the cosmetic of Comparative Formulation 4 and to that of the chemical preservative contained in the cosmetic of Comparative Formulation 5. Thus, it was established that the silver/polymer nanocomposites proposed by the present invention exhibit excellent preservative activity.

<Formulations 5-7 and Comparative Formulations 6~8> Nutrient toilet waters (Lotions) In order to determine the preservative activity of the silver/polymer nanocomposites prepared in Example 2, depending on its amount in a nutrient toilet water, nutrient toilet waters were formulated in the compositions of Table 6. For comparison, Comparative Formulation 7 containing the same content of Ag nanoparticles, prepared in Comparative Example 3 was formulated and its preservative activity was compared. Further, Comparative Formulation 8 containing conventional chemical preservatives, i.e. methylparaben, propylparaben and imidazohdinyl urea was formulated. [Table 6]

<Test 3> Preservative Activity Test Preservative activity test was performed by the same procedure as described in Test 1, and the results are shown in Table 7. [Table 7]

- : For 8 weeks, no damp smell, no spawning and no spore germination and good condition + : Within 4 weeks, fungi were observed on the wall or the cover of the container

+++ : Within 4 weeks, damp smell and fungi were observed on the whole surface of the test product As shown in Table 7, only the addition of 0.1 wt% or more of the silver/polymer nanocomposites showed high preservative activity. Thus, it was established that the silver/polymer nanocomposites proposed by the present invention can exhibit as strong preservative activity as the conventional chemical preservatives, in nutrient toilet water.

<Formulations 8-10 and Comparative Formulations 9-11> Creams In order to determine the preservative activity of the silver/polymer nanocomposites prepared in Example 2, depending on its amount in a cream, creams were formulated in the compositions of Table 8. For comparison, Comparative Formulation 10 containing the same content of Ag nanoparticles, prepared in Comparative Example 3, was formulated and its preservative activity was compared. Further, Comparative Formulation 11 containing conventional chemical preservatives, i.e. methylparaben, propylparaben and imidazohdinyl urea was formulated. [Table 8]

<Test 4> Preservative Activity Test Preservative activity test was performed by the same procedure as described in Test 1, and the results are shown in Table 9. [Table 9]

+++ : Within 4 weeks, damp smell and fungi were observed on the whole surface of the test product As shown in Table 9, only the addition of 0.1 wt% or more of the silver/polymer nanocomposites of Example 2 or of the Ag nanoparticles of Comparative Example 3 showed high preservative activity. This indicates that the silver/polymer nanocomposites can effectively dissociate into silver ion in aqueous phase. The preservative activity was proportional to the content of silver incorporated. Further, as confirmed in Comparative Formulations 5, 8 and 11, the silver/polymer nanocomposites showed as strong preservative activity as the conventional chemical preservatives i.e. methylparaben, propylparaben and imidazohdinyl urea.

Experimental Example 3> Storage stability of silver/polymer nanocomposites In order to confirm if the initial activity may be maintained after long-term storage, the cosmetics of Formulations 5 to 7 and Comparative Formulation 6 were stored for 90 days at room temperature, and then preservative activity test was conducted again. The a preservative activity test was performed by the same procedure as described in said Test 1, and the results are shown in Table 10. [Table 10]

<Description of Grade> - : For 8 weeks, no damp smell, no spawning and no spore germination and good condition

+ : Within 4 weeks, fungi were observed on the wall or the cover of the container ++ : Within 4 weeks, damp smell and fungi were observed on part of the surface of the test product

+++ : Within 4 weeks, damp smell and fungi were observed on the whole surface of the test product As shown in Table 10, the silver/polymer nanocomposites contained in the cosmetics, after long-term storage, showed the same preservative activity as that shown directly after the preparation thereof. This indicates that the silver/polymer nanocomposites can effectively dissociate into silver ions in a cosmetic formulation during long period. Further, the discoloration behaviors of the cosmetics of Formulation 6 and

Comparative Formulation 7, after long-term storage, were investigated and the results are shown in Figure 4. In general, Ag nanoparticles undergo dissociation into silver ions and the re-reduction process repeatedly, and cause cohesion therebetween, to form Ag hetero-particles after long-term storage. The dissociation into silver ions is necessary to improve the preservative activity. Unfortunately, silver hetero-particles formed by re-reduction and cohesion may cause discoloration. The same results were observed in Comparative Formulation 7. After long-terai storage, the color changed into dark brown and the characteristic absorbance band at 410nm was shifted to the visible region, which was confirmed by ultraviolet spectrum. This behavior of Ag nanoparticles makes it impossible to be applied to cosmetic compositions. On the other hand, no change in appearance of Formulation 6 containing the silver/polymer nanocomposites was detected, after long-term storage. It is assumed that this is because the silver/polymer nanocomposites may effectively dissociate into silver ions through porous channels and thereby can exhibit strong preservative activity, and the silver hetero-particles formed by re-reduction and cohesion may be preferentially re-deposited onto the porous surface having functional group. As shown by the ultraviolet spectra of Figure 4, ultraviolet/visible rays were blocked from the beginning by the porous polymer support and the absorbance band at 410nm was not detected, and after long-term storage, the initial absorbance behavior was detected unchanged. This directly demonstrates that no Ag particles were present in the outer phase.

INDUSTRIAL APPLICATION OF THE INVENTION

As above described, the silver/polymer nanocomposites provided by the present invention may not cause general discoloration and cohesion by silver nanoparticles and thereby can be used as a preservative having strong antimicrobial activity, and can be incorporated into various cosmetic compositions to enable long-term storage thereof, not using chemical preservatives which might cause skin irritation and allergy reaction.

Claims

1. Silver/polymer composite nanospheres prepared by depositing silver nanoparticles on the surface of porous polymer particles.

2. The silver/polymer composite nanospheres according to Claim 1, wherein said silver nanoparticles are deposited on the surface of said porous polymer particles in an amount of 0.001 to 30% by weight based on the total weight of polymer.

3. The silver/polymer composite nanospheres according to Claim 1, wherein said porous polymer particles have a particle size of 0.01 to 1,000 μm.

4. A process for preparing silver/polymer composite nanospheres, which comprises the following steps of (1) dissolving monomer, crosslinking agent and initiator in a solvent to give a monomer solution; (2) emulsifying said monomer solution in the presence of dispersion stabilizer to give an emulsion; (3) polymerizing said emulsion and then removing the solvent to collect porous polymer particles; and (4) depositing silver nanoparticles formed by reducing silver salts with a reducing agent, on the surface of the porous polymer particles collected in step (3).

5. The process according to Claim 4, wherein said monomer in the step (1) is one or more selected from the group consisting of styrene; acrylate; vinyl acetate; vinyl ether; unsaturated carboxylic acid including maleic acid; alkyl(meth)acrylamide; (meth)acrylonitrile; and their derivatives.

6. The process according to Claim 4, wherein said crosslinking agent in the step (1) is one or more selected from the group consisting of allyl compounds including divinylbenzene and diallylphthalate; (poly)alkylene glycol di(meth)acrylate including (poly)ethylene glycol di(meth)acrylate; urethane acrylate; epoxy acrylate; and their derivatives.

7. The process according to Claim 4, wherein said initiator in the step (1) is one or more selected from the group consisting of peroxides including benzoyl peroxide; azo compounds including 2,2-azobisisobutyronitrile; and their derivatives.

8. The process according to Claim 4, wherein said solvent in the step (1) is one or more selected from the group consisting of linear alkanes such as hexane; alcohols having from 4 to 10 carbon atoms such as butanol; alkyl esters having 7 or more carbon atoms such as n-hexyl acetate; aliphatic ketones; aromatic hydrocarbons such as toluene; chlorine compounds such as methylene chloride; and their derivatives.

9. The process according to Claim 4, wherein said dispersion stabilizer in the step

(2) is one or more selected from the group consisting of gelatin, starch, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alkyl ether, polyvinyl alcohol and polydimethyl siloxane/polystyrene block copolymer.

10. The process according to Claim 4, wherein said silver salt in the step (4) is one or more selected from the group consisting of silver acetate, silver bromide, silver carbonate, silver chloride, silver citrate, silver cyanide, silver fluoride, silver iodide, silver nitrate, silver nitrite, silver phosphate, silver sulfate and silver sulfide.

11. The process according to Claim 4, wherein said reducing agent in the step (4) is one or more selected from the group consisting of hydrazine, LiAlBH₄, NaBH₄, and ethylene oxide and its derivatives.

12. A cosmetic preservative using the silver/polymer composite nanospheres according to any one of Claims 1 to 3.

13. A cosmetic composition containing the cosmetic preservative according to Claim 12 in an amount of 0.01 to 5% by weight based on the total weight of the composition.

14. The cosmetic composition according to Claim 13, which is formulated into skin softeners, nutrient toilet waters, massage creams, nutrient creams, gels, packs, essences, lipsticks, make-up bases, foundations, lotions, ointments, creams, patches, aerosols, sprays, powders, eye shadows or body cleansers.

15. A cosmetic preservative using the silver/polymer composite nanospheres prepared by the process according to any one of Claims 4 to 11.

16. A cosmetic composition containing the cosmetic preservative according to Claim 15 in an amount of 0.01 to 5% by weight based on the total weight of the composition.

17. The cosmetic composition according to Claim 16, which is formulated into skin softeners, nutrient toilet waters, massage creams, nutrient creams, gels, packs, essences, lipsticks, make-up bases, foundations, lotions, ointments, creams, patches, aerosols, sprays, powders, eye shadows or body cleansers.