METAL PARTICLE

Abstract: Disclosed is a metal particle having a maximum dimension of not more than 1 mm surface-treated with an aqueous solution containing phosphate ions, soluble ions of vanadium and oxygen. This particle can be a metallic pigment having excellent brightness retention and wetting properties to a binder resin.

Description: Field of the Invention The present invention relates to metal particles, especially a metal pigment. Background of the Invention Generally, metal particles, such as zinc particles, iron particles, stainless steel particles, copper-zinc-nickel alloy particles, resin or glass particles plated with metal, corrode in the presence of water, oxygen or electrolyte ions. It is required that the metal particles are, therefore, carefully handled. For example, they are stored in a nitrogen blanket or an organic solvent in order to separate from corrosive conditions. If the metal particles corroded in a high corrosion rate, hydrogen gas which is difficult to deal with would be produced. Also, if they are formulated into a coating composition, they corrode by an invasion of water, oxygen or an electrolyte into a coating to result in a decline of the coatings. In order to prevent the corrosion, it is proposed to allow the metal particles to contact with a chromate ion. The chromate ion has two functions. One is an oxidizer function whereby the chromate ion (CrO₄²⁻) is reacted with a metal atom, such as Fe to form stable gamma-Fe₂ O₃, and the other is a deposition function whereby the chromate ion is reduced to form a chromium oxide, for example Cr₂O₃ which is deposited on a metal surface. According to these two functions, a physical barrier film is formed on the metal surface to develop excellent corrosion preventive properties. However, the chromium (VI) having high corrosion preventive properties is toxic to human body and therefore very limited in use by several regulations in Japan. Accordingly, many efforts have been paid to develop a corrosion preventive agent which is not or little toxic to human body. For example, phosphate materials, especially zinc phosphate, silicophosphate, aluminum condensed phosphate and the like are now studied and some of them are commercially available. The phosphate materials, however, have only the deposition function whereby the phosphate materials are reacted with metal to produce a material protecting the metal substrate, and have not the oxidizer function. The phosphate materials have low corrosion preventive properties in comparison with the above mentioned chromate ions. The present inventors proposed that the oxidizer function which was lack in the phosphate materials was compensated for a soluble ion of vanadium (see Japanese Patent Application Ser. No. 204794/1986, Japanese Kokai Publication 60294/1988). The inventors further develop a novel surface treatment process for aluminum flake pigment particles. Summary of the Invention The present invention provides an aluminum flake pigment particle having a maximum dimension of not more than 1 mm surface-treated with an aqueous solution containing phosphate ions, soluble ions of vanadium and oxygen, as claimed in claim 1. Detailed Description of the Invention The soluble ions of vanadium supplement the oxidizer function which lacks in the phosphate ions. The vanadium ions form redox couples under the corrosive conditions containing water and oxygen, thereby a redox couple indicates a noble redox potential and then fulfils the oxidizer function. On the other hand, as mentioned previously, the phosphate ions form, under the corrosive conditions, a deposited film (probably FePO₄), thus providing the deposition function. Accordingly, these two species of ions are indispensable in embodying the present invention, and the effect of the invention is not attained when even one of these two species is absent. The soluble ions of vanadium used in the present invention are monomeric ions or polymeric ions having a trivalent, tetravalent and pentavalent vanadium element, including V³⁺, VOH²⁺, VO⁺, HV₂O₅⁻, VO²⁺ H₃V₂O₇⁻, H₂VO₄⁻, HVO₄²⁻, VO₄³⁻, HV₂O₇³⁻, V₂O₇⁴⁻', V₃O₉³⁻, V₄O₁₂⁴⁻, H₂V₁₀O₂₈⁴⁻, H₂V₁₀O₂₈⁵⁻, V₁₀O₂₈⁶⁻ and the like. In essence, these ions of vanadium are categorized into vanadium ions, vanadyl ions, orthovanadate ions and condensed vanadate ions. Vanadate ions and condensed vanadate ions are preferable. These two ion species usually exist in an aqueous solution as a mixture, as known to the art. When a pH is around neutral (within a range of 5 to 9), the condensed vanadate ions prevail in the solution and a trace amount of orthovanadate ions are present, because the orthovanadate ions are condensed with each other in an aqueous solution. Typical examples of the condensed vanadate ions are pyrovanadate ions, metavanadate ions, trivanadate ions, tetravanadate ions, hexavanadate ions, decavanadate ions and the like. Examples of the phosphate ions are orthophosphate ions, pyrophosphate ions, tripolyphosphate ions, higher condensed phosphate ions, trimetaphosphate ions, tetrametaphosphate ions or higher condensed metaphosphate ions. The phosphate ions are present in an aqueous solution in various forms due to condensation degree and pH. Generally, the phosphate ions are condensates in an aqueous solution. To supply such soluble ions of vanadium and phosphate ions, an ion carrier such as an ion-exchange resin or inorganic ion exchange material (for example, hydrotalcite) may be allowed to absorb these ions. A corrosion preventive agent, which is prepared by mixing a phosphate ion source and a source of soluble ion of vanadium, or by baking or melting the phosphate ion source and source of soluble ion, of vanadium, may be added in an aqueous solution. Such a corrosion preventive agent, especially a corrosion preventive pigment, are disclosed in Japanese Patent Application Ser. Nos. 36191/1987, 36192/1987, 36189/1987 and 36190/1987 (corresponding to EP-A-0 259 748). It is necessary that there is oxygen in the aqueous solution. It is not always necessary to provide oxygen in the aqueous solution. It is sufficient to use natural or deionized water, because such water contains dissolved oxygen. If the treatment is carried out in a condition having no oxygen, it is necessary to introduce oxygen in the aqueous solution. A method, wherein the aluminum flake pigment particles are surface-treated with the aqueous solution containing the soluble ions of vanadium, phosphate ions and oxygen, may comprise spraying the aqueous solution to the metal particles floated in air. Preferably, the aluminum flake pigment particles may be immersed in the aqueous solution for treatment, especially under mixing or ultrasonic vibration by which agglomeration of the particles is effectively prevented for a uniform treatment. A maximum dimension of the particles can be not more than 1 mm, preferably within the range of 1 to 100 micron. The aluminum pigment generally reacts with water or many electrolytes in a paint to significantly reduce brightness and to become a color of black, so that it cannot be usable for a pigment. The aluminum pigment treated as disclosed in the present invention has excellent brightness retention and enhances wetting properties to a binder component in the coating composition. The treatment condition is not limited if the aqueous solution for treatment contains the soluble ions of vanadium, phosphate ions and oxygen. The treating condition has a pH of 5 to 9. The amount of the soluble ions of vanadium and phosphate ions are respectively 0.001 to 0.1 mole/liter, preferably 0.05 to 0.1 mole/liter. Amounts outside of the above range deteriorate the technical effect of the present invention. A temperature for treatment is not specifically limited. A high temperature reduces the treatment period. The aqueous solution for treatment may further contain other additives, such as surfactant; and cations, such as calcium ions and magnesium ions. The surface treated aluminum flake pigment particles have a very thin film, a so-called passive film, on the surface, but maintains its features as particles. The particle can be easily handled and can be stored in the air. The treatment of the present invention prevents a color change of the aluminum flake pigment particles for a long time. The treatment of the present invention enhances wetting properties to a resin binder and reduces a period of time for a dispersing process. Examples The present invention is illustrated by the following examples which, however, are not to be construed as limiting the invention to their details. Example 1 The present example shows the technical effect of the treatment of the present invention. 0.05 mole/liter of orthophosphoric acid was added to a 0.05 mole/liter aqueous solution of sodium orthovanadate and a pH was adapted to 7 by sodium hydroxide to form an aqueous solution A for treatment. Another aqueous solution B only containing 0.05 mole/liter of orthophosphoric acid was prepared in a similar manner. The aluminum flake pigment particles shown in Table 1 were immersed in the aqueous solutions A and B and deionized water for one hour and then rinsed with deionized water to dry. The obtained particles were allowed to stand in the air at 40°C for 7 days and its color was visually evaluated. The result is shown in Table 1. Examples 2 to 8 The present invention shows technical effects of an aluminum flake pigment surface treated according to the present invention. An aluminum flake pigment was surface treated as generally described in Example 1, with the exception that a pH of the aqueous solution and concentrations of the phosphate ions and vanadate ions were changed as shown in Table 2. The obtained aluminum flake pigment was formulated into an aqueous coating composition, of which preparation was described after Table 2. An amount of hydrogen gas generated from the coating composition was measured by collecting in a flask. Also, the aqueous coating composition was poured in a test tube and allowed to stand for 10 day at 50 °C. The precipitated aluminum flake was visually evaluated. Further, the aqueous coating composition was spray coated as described in a coating test after Table 2 and its brightness of the cured coatings was visually evaluated. Evaluation was made as follow: An aluminum flake pigment coated with a conventional organic phosphate was made standard. By comparing with the standard, good, excellent, bad and very bad were determined. The result of the test is shown in Table 2 Preparation of coating composition (Preparation of polyester resin) A two liter flask equipped with a stirrer, a nitrogen-introducing tube, a temperature controlling apparatus, a condenser and a decanter was charged with 130 parts by weight of bishydroxyethyl taurine, 134 parts by weight of neopentyl glycol, 236 parts by weight of azelaic acid, 186 parts by weight of phthalic anhydride, and 27 parts by weight of xylene, and heated to start a reaction. Water produced by the reaction was azeotropically distilled together with xylene. The mixture was heated to 190 °C over about 2 hours after commencing reflux and continued to mix and distill until an acid value corresponding to carboxylic acid was 145. The mixture was then cooled to 140 °C and 314 parts by weight of Cardura E 10 (glycidyl ester of versatic acid available from Shell Chemical Company) was added for 30 minutes while maintaining 140 °C. Mixing was continued for 2 hours to terminate the reaction. The obtained polyester resin had an acid value of 59, a hydroxyl value of 90 and Mn 1054. (Preparation of resin particles) A one liter reaction vessel equipped with a stirrer, a condenser and a temperature controlling apparatus was charged with 282 parts by weight of deionized water, 10 parts by weight of the polyester resin obtained above and 0.75 parts by weight of dimethylethanolamine to form a mixture. a solution containing 4.5 parts by weight of azobiscyanovaleric acid, 45 parts by weight of deionized water and 4.3 parts by weight of dimethylethanolamine was added to the mixture, to which a solution containing 70.7 parts by weight of methyl methacrylate, 94.2 parts by weight of n-butyl acrylate, 70.7 parts by weight of styrene, 30 parts by weight of 2-hydroxyethyl acrylate and 4.5 parts by weight of ethylene glycol dimethyl acrylate was added dropwise for 60 minute. After addition, a solution containing 1.5 parts by weight of azobiscyanovaleric acid, 15 parts by weight of deionized water and 1.4 parts by weight of dimethylethanolamine was added and mixed at 80 °C for 60 minutes to obtain an emulsion having non-volatile 45 %, pH 7.2, viscosity 92 cps (25 °C) and a particle size of 0.165 micron. The emulsion was spray-dried to obtain resin particles having a particle size of 0.3 micron. 100 parts by weight of the particles were dispersed in 200 parts by weight of xylene to obtain a xylene dispersion. (Preparation of a resin for metallic coating composition) A reaction vessel equipped with a stirrer, a temperature controlling apparatus and a condenser was charged with 76 parts by weight of ethylene glycol monobutyl ether and 61 parts by weight of a monomer solution (containing 45 parts by weight of styrene, 63 parts by weight of methyl methacrylate, 48 parts by weight 2-hydroxyethyl methacrylate, 117 parts by weight of n-butyl acrylate, 27 parts by weight of methacrylic acid, 3 parts by weight of laurylmercaptane and 3 parts by weight of azobisisobutylonitrile) at 120 °C and mixed for one hour. 28 parts by weight of dimethylethanolamine and 200 parts by weight of deionized water was added to the resultant mixture to obtain an acrylic varnish having non-volatile 50 % and Mn 6,000. The resin had a OH value of 70, and an acid value of 58. (Preparation of metallic coating composition) A mixture of 140 parts by weight of the resin varnish mentioned above, 30 parts by weight of the resin dispersion, 10 parts by weight of aluminum pigment and 30 parts by weight of Cymel 303 as a cross-linking agent was diluted with deionized water up to 25 to 30 seconds of No.4 Ford Cup (20 °C) to form a metallic coating composition. (Preparation of clear coating composition) A polymer was prepared as generally described in the above (Preparation of a resin for metallic coating composition), using 65.8 parts by weight of n-butyl acrylate, 11.8 parts by weight of methyl methacrylate, 16.2 parts by weight of hydroxyethyl methacrylate, 6.1 parts by weight of methacrylic acid and 5 parts by weight of azobisisobutylonitrile. The polymer was neutralized with dimethylethanolamine and then diluted with water to obtain a resin varnish having non-volatile 50 %. To the obtained resin varnish, a cross-linking agent (hexamethoxymethylolmelamine available from Mitsui Toatsu Company as "Cymel 303" was added in a solid/resin ratio of 70/30 and diluted up to 30 to 35 seconds (20 °C) of No.4 Ford cup to obtain an aqueous clear coating composition. (Coating test) The metallic coating composition was spray-applied to an intermediate coated steel panel in a thickness of 20 micron at 23 °C and 60 % relative humidity, on which the clear coating composition was spray-applied in a thickness of 30 micron in a same condition mentioned above. The former was coated in two stages at an interval of one minute and then it was dried at 80 °C for 5 minutes. The latter was then coated in one stage and allowed to a setting of 7 minutes. The coated panel was cured at 150 °C for 20 minutes to obtain a sample panel.

Claims: An aluminum flake pigment particle for metallic paint, of a maximum dimension of not more than 1 mm, having excellent brightness retention and resistance to corrosion, which has been treated with an aqueous solution containing phosphate ions, soluble ions of vanadium and oxygen such as to render the aluminum flake resistant to corrosion, said aqueous solution containing 0.001 to 0.1 mole/liter of the phosphate ions, 0.001 to 0.1 mole/liter of the soluble ions of vanadium and having a pH of 5 to 9. The aluminum flake pigment particle according to Claim 1 wherein said aluminum flake pigment particle was prepared by spraying said aqueous solution onto aluminum flakes, or immersing aluminum flakes in said aqueous solution, said aluminum flakes not having been treated with an alkaline solution. The aluminum flake pigment particle according to Claim 1 which has been treated with said aqueous solution at a temperature and time sufficient to produce a corrosion resistant film on the surface of the aluminum flakes.

Inventors: KUWAJIMA, TERUAKI, ODA, MITSUYUKI, OKAI, TOSHIHIRO, OKUMURA, YOSHIAKI, YAMAMOTO, TAKASHI
Applicants: NIPPON PAINT CO., LTD.
Application year: 1987
Main classification: C23C22
IPC codes: C09C3, B22F1, C23C22, C09C1