Antimicrobial powders and method for making same

Abstract: The antimicrobial powders of the present invention is obtained by supporting at least one antimicrobial metal of copper, zinc and alloys thereof on the surface of hydrous titanium oxide or titanium oxide particles by electroless plating, vapor deposi­ tion, compression mixing, mixing and reducing, and thermal decomposition of compound. These powders are used to provide antimicrobial resin compositions, antimicrobial rubber compositions, antimicrobial glass compositions and antimicrobial coating compositions.

Description: BACKGROUND OF THE INVENTION. FIELD OF THE INVENTION The present invention relates to a method for producing antimicrobial powders which comprises compression mixing an antimicrobial metal with hydrous titanium oxide or titanium oxide particles to support said antimicrobial metal on the surface of said particles. DESCRIPTION OF THE RELATED ART It is well known that metals such as copper and silver have antimicrobial properties as so-called oligodynamic action. For example, there have been proposed utilization thereof as therapeutic or preventive medicines which use copper ion generated from various soluble copper salts, copper complex compounds, etc., and bactericidal filters, algicidal filter, algicidal net, bactericidal and deodorant cloths or leathers made from superfine copper fibers produced from copper metal. Specifically, Japanese Patent Kokai No. 88109/88 discloses an antibacterial composition comprising a support of an oxide of Ti, Mg, Al or the like on which silver chloride is applied. Recently, materials, industrial products and constructions have suffered from various damages by microorganisms such as molds and bacteria and other harmful organisms and many proposals have been made in an attempt to prevent these damages. One of them is the use of the above metallic copper fibers and besides various preventive means using antimicrobial properties of the above-mentioned metals have been extensively studied. For example, it has been attempted to support a metal component on solid powders such as zeolite by ion exchange reaction. (cf. Japanese Patent Kokai No. 133235/84). However, the aforementioned silver chloride-supporting oxides and metal component-supporting zeolite powders have the following defects. That is, it is difficult to make them in the form of fine particles; The supported metal component readily falls off from the surface of particles; They are not sufficient in dispersibility in media such as paint coating compositions, resin moldings, resin films, and coating compositions for paper processing; and addition amount must be increased in order to obtain sufficient antimicrobial effect and as a result, color tone of coated articles or molded articles applied therewith is damaged and desired color cannot be obtianed. Thus, improvements thereof has been demanded. In case of appliances and high-grade household furnitures subjected to antimicrobial treatment which require beautiful coloring, the above improvement has been especially strongly desired. EP-A-0 251 783 discloses an antimicrobial composition for topical use or for incorporation into a coating wherein silver compounds are deposited on an oxidic support material, and a process for the preparation thereof comprising deposition of silver compounds under conditions of controlled nucleation and growth on the support material. EP-A-0 190 504 discloses antimicrobial compositions comprising silver as the antimicrobial agent and an hydratable or hydrated oxide as a promoter to enhance the antimicrobial effect. Metallic silver may be supported on e.g. titanium oxide. Silver and the oxide may be present therein as an admixture or silver may be deposited on the oxide. Deposition of silver on the oxide is effected by using the well-known procedure with Fehling's solution or by precipitating silver chloride from a silver nitrate solution onto the oxide which then is believed to be reduced to silver metal by the action of light. SUMMARY OF THE INVENTION The object of the present invention is to provide a method for producing antimicrobial powder which is free from the above problems and which has superior antimicrobial properties and furthermore, to provide a method for producing an antimicrobial composition excellent in color tone by adding or applying the antimicrobial powders to various media. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors have made various studies on enhancement of added value of hydrous titanium oxide or titanium oxide powders as functional material or on making composite materials from the hydrous titanium oxide or titanium oxide. In the course of the study, they have given notice to application of antimicrobial powders as a substrate and have made further studies to find that these titanium oxide powders are conspicuously superior in adhesion of antimicrobial metal component to the surface thereof and hence retention of the antimicrobial effect can be prolonged and besides coloring property of compositions comprising titanium oxide powders on which antimicrobial metal is supported can be further improved. The present invention has been accomplished based on this finding. That is, the present invention resides in a method for producing antimicrobial powders, characterized by comprising compression mixing at least one antimicrobial metal selected from the group consisting of copper, zinc and copper and/or zinc based alloys with hydrous titanium oxide or titanium oxide particles to support said antimicrobial metal on the surface of hydrous titanium oxide or titanium oxide. The hydrous titanium oxide or titanium oxide (hereinafter referred to as "substrate particles") which supports the antimicrobial metal component in the present invention includes, in addition to so-called hydrous titanium dioxide represented by TiO₂·nH₂O, various hydrated titanium dioxides, ordinary titanium dioxide having Ti:O of nearly 1:2, so-called lower titanium oxide having various Ti:O, titanium-nickel-antimony system and titanium-chromium-antimony mainly composed of titanium dioxide as constituting component, and various titanium oxide composite pigments and synthetic rutile pigments. These substrate particles have an average particle size of normally 0.01-3 µm, desirably 0.02-1 µm and more desirably 0.03-0.4 µm. These substrate particles may be those which are produced by various methods such as, for example, (1) titanium dioxide powders obtained by vapor phase oxidation decomposition of titanium tetrachloride, (2) hydrous titanium dioxide obtained by hydrolysis of a titanium sulfate solution, titanium tetrachloride solution or organotitanium compound solution, if necessary, in the presence of a nucleating seed, (3) titanium dioxide powders obtained by calcining hydrous titanium dioxide, (4) various lower titanium oxide powders obtained by subjecting to thermal reduction treatment the hydrous titanium dioxide precipitate or titanium dioxide powders obtained in the above (1), (2) or (3), and (5) titanium oxide composite pigments obtained by adding a coloring metal component to the hydrous titanium oxide precipitate obtained in the above (2), followed by reaction with heating. The antimicrobial metal supported on the substrate particles in the present invention includes metallic copper, metallic zinc, and copper and/or zinc-based alloys such as a Cu-Zn alloy, Cu-Ag alloy, Cu-Sn alloy, Cu-Al alloy, Zn-Sn alloy, Zn-Sn-Cu alloy, Zn-Al-Cu-Mg alloy and the like. These metals may be supported alone or in combination of two or more. Amount of the metal component supported is normally 0.001-35%, preferably 0.01-30% in terms of metal based on the weight of substrate particles. If the amount is less than the above range, desired antimicrobial effect cannot be exhibited and if more than the range, not only this is disadvantageous on cost, but also dispersibility in medium to be imparted with antimicrobial property and coloring property are sometimes damaged. Supporting of the antimicrobial metal on the substrate particles in the present invention can be performed by a method according to which the substrate particles and the antimicrobial metal powders are charged in dry- or wet-type compressing grinder such as a ball mill or edge runner mill and are compression mixed therein to support the antimicrobial metal on the surface of the substrate particles. When the supporting method is conducted, it is desired to carry out them in an inert gas atmosphere such as nitrogen gas so as to prevent oxidation as far as possible. The antimicrobial powders prepared according to the present invention are useful against various microorganisms. As these microorganisms, mention may be made of, for example, Gram-positive bacteria (such as Bacillus subtilis, Staphylococcus aureus, and Streptococcus pyogenes), Gram-negative bacteria (such as Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, Serratia marcescens, Proteus morganii, Proteus Vulgaris, Pseudomonas aeruginosa, and Vibrio parahaemolyticus), trichophyton (such as Trichophyton mentagraphytes and Trichophyton rubrum), eumycetes (such as Candida albicans), molds (such as Penicillium chrysogenum, Penicillium citrinum, Cladosporium fulvum, Aspergillus fumigatus, Aspergillus niger and Cladosporium herbarum). The resulting antimicrobial powders can be added to various resins, rubbers, glasses, etc. to produce antimicrobial compositions or can be used for antimicrobial treatment of industrial and household electrical equipments, furnitures, furnishing materials, packaging materials for foods by various methods known per se or can be utilized as antimicrobial agents for various environmental health facilities or equipments. In the antimicrobial powders obtained by the present invention, antimicrobial metal component is firmly supported on the surface of substrate particles and increase of retentivity of antimicrobial effect can be further expected. Besides, they have excellent optical characteristics such as high hiding power inherent to the titanium dioxide of the substrate particles and furthermore-good dispersibility and are high in industrial value as antimicrobial property imparting materials and coloring materials in a wide variety of fields. The present invention will be explained further by the following examples and comparative examples. Example 1 240 Grams of the rutile-type titanium dioxide powders prepared by vapor phase oxidation decomposition of titanium tetrachloride and having the composition as shown in Table 1 used as substrate particles were suspended in water to obtain an aqueous concentrated slurry (237 g/l of solid content). 250 Milliliters of this slurry was taken and thereinto was introduced 10 g of blass powders (Cu+Zn alloy; BRA-AT-200 manufactured by Fukuda Kinzoku Haku Kogyo Co.) and this was well mixed by Henschel mixer. Thereafter, the mixture was subjected to compression mixing for 24 hours in a magnetic ball mill (internal volume of the mill was 1 liter; filled with 500 ml of alumina balls of 10 mm in diameter; amount of slurry was 250 ml and number of revolution was 100 rpm) to support the brass alloy on the surface of the substrate particles. After completion of the ball mill treatment, the slurry was taken out and diluted and repeatedly subjected to sedimentation separating to fractionate the titanium dioxide particles from the brass particles. The titanium dioxide slurry after completion of the fractionation was subjected to filtration, washing with water and drying to obtain the objective antimicrobial powders. Crystal form Rutile Particle size (µm) 0.2 ∼ 0.4 True specific gravity 4.2 Bulk specific gravity (gr/cm³) 0.5 ∼ 0.7 Oil absorption 12 ∼ 14 Analysis TiO₂ (%) 99.8 Al₂O₃ (%) 0.002 SiO₂ (%) 0.02 Fe₂O₃ (%) 0.0034 P₂O₃ (%) 0.000 Na₂O (%) 0.005 Nb₂O₃ (%) 0.00 SO₃ (%) 0.00 H₂O (%) 0.04 Igloss (%) 0.09 Example 2 The procedure of Example 1 was repeated except that 10 g of copper particles (CU-AT-200 manufactured by Fukuda Kinzoku Haku Kogyo Co.) were introduced into 250 ml of the concentrated aqueous slurry of substrate particles used in Example 1 to obtain the objective antimicrobial powders comprising metallic copper supported on the surface of substrate particles. The powders having antimicrobial metal supported thereon obtained in Examples 1 and 2 were respectively put in containers, the atmosphere of which was replaced with nitrogen gas. Properties of these samples are shown in Table 2. Referential Example 1 To 10 g of one kind (A₁) of antimicrobial powders shown in Table 2 was added 10 ml of toluene. After sufficient stirring, thereto was added 4 g of acrylic resin (ACRYDICK manufactured by Dainippon Ink & Chemicals Inc.), followed by further stirring and mixing. All of this mixture was charged in a paint shaker manufactured by Red Devils Co. (internal volume: 90 cm³ and filled with 40 g of glass beads of 1.0 mm in diameter) and mixed and dispersed by vertical motion for 30 minutes. The mixture was allowed to pass through a mesh to remove glass beads to obtain the following coating composition. Properties of coating composition PVC (Volume content of pigment) 67% SVC (Volume content of solid) 25% Viscosity 250 c.p. This coating composition was hand coated on a polypropylene synthetic paper (about 100 µm thick: YUPO manufactured by Oji Yuka Co.) by a doctor blade (depth 50 µm). This was allowed to dry to the touch and left to stand overnight at 80°C and then cut out into a circle (23 mm in diameter) to obtain a coated shaped product (B₁) of about 14 µm in dry film thickness and about 113 µm in total thickness. Referential Example 2 To 20 g of antimicrobial powders (A₁) shown in Table 2 was added 1 g of ethyl cellulose, followed by sufficient stirring. Then, 1 g of the mixture was charged in a concentric cylindrical mortar (having super hard alloy lining; inner diameter: 23 mm and outer diameter: 115 mm in diameter manufactured by Kikusui Seisakusho Co.) and subjected to hydraulic pressing by means of a columnar pestle (manufactured by Kikusui Seisakusho Co.; outer diameter: 23 mm). Pressing procedure was as follows: Pressure was increased at 50 kgG/cm² per 1 minute and whenever increment of pressure reached 400 kgG/cm², the pressure at this time was kept for 10 minutes and then hydraulic pressure was released. Subsequently, the mortar was transferred onto a stair tread and hydraulic pressure was again applied to gradually press down the pestle to draw out the sample from the bottom of the mortar. In this way, a compression shaped product (C₁) with an outer diameter of 23 mm and a thickness of 1.0 mm was obtained. Referential Test Example Antimicrobial tests were conducted using the antimicrobial shaped products (B₁, C₁) obtained in Referential Examples 1 and 2 as test samples and coated shaped product (B₀) and compression shaped product (C₀) prepared by treating titanium dioxide supporting no antimicrobial metal on the surface (substrate particles in Table 1) in the same manner as in Referential Example 1 and 3 as blank samples. Three kinds of bacteria, namely, Staphylococcus aureus, Salmonella enteritidis and Escherichia coli were used for the tests. Test method was as follows: One or two of each sample were put in a petri dish containing 100 ml of sterilized physiological saline to which 0.10% of peptone was added (in case of two samples were used, these were put side by side). Then, thereon were inoculated a given amount of the bacteria and antimicrobial activity of each sample was evaluated by counting the number of bacteria every 4 hours at a culturing temperature of 35°C relative to the number of bacteria just after inoculation. The results are shown in Table 3 (in case of using one sample) and Table 4 (in case of using two samples).

Claims: A method for producing antimicrobial powders which comprises compression mixing at least one antimicrobial metal selected from copper, zinc and copper and/or zinc based alloys with hydrous titanium oxide or titanium oxide particles to support said antimicrobial metal on the surface of said particles. The method of claim 1 wherein said antimicrobial metal is supported on the surface of said particles in an amount of from 0.001 to 35% by weight based on the weight of said particles. The method of claim 1 or 2 wherein said copper and/or zinc based alloys are selected from a Cu-Zn alloy, a Cu-Ag alloy, a Cu-Sn alloy, a Cu-Al alloy, a Zn-Sn alloy, a Zn-Sn-Cu alloy and a Zn-Al-Cu-Mg alloy. The method of any of claims 1 to 3 wherein said hydrous titanium oxide or titanium oxide particles have a size of from 0.01 to 3 µm, preferably 0.02 to 2 µm, and particularly 0.03 to 0.4 µm. The method of any of claims 1 to 4 wherein said method is carried out in an inert gas atmosphere.

Inventors: ICHIMURA KENICHI, MIZUKOSHI SADANORI, MURAKAMI HAJIME, YAMADA NOBUTOSHI, ICHIMURA, KENICHI, MIZUKOSHI, SADANORI, MURAKAMI, HAJIME, YAMADA, NOBUTOSHI
Applicants: ISHIHARA SANGYO KAISHA, ISHIHARA SANGYO KAISHA, LTD.
Application year: 1989
Main classification: A01N59
IPC codes: A01N25, A01N59, C08K9, C09D5, C01G23, C03C14