Liquid rust proof film-forming composition and rust proof film-forming method

Abstract: A liquid rust proof film-forming composition comprises (A) an oxidative substance, (B) a silicate and/or silicon dioxide and (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Ce, Sr, V, W and Mo; and oxymetal anions and fluorometal anions thereof. The composition can be used in a method for forming a rust proof film on a metal substrate which comprises the step of immersing the metal substrate in the composition. The composition and the methods form an excellent rust proof film on the surface of metal substrates without using any chemical substance harmful to environment such as hexavalent chromium.

Description: The present invention relates to a rust proof film-forming method for treating the surface of metal materials to thus effectively keep the same from rusting and a liquid rust proof film-forming composition for use in the method. There have been used a solution containing hexavalent chromium in most of the conventionally proposed techniques for treating the surface of metals to thus effectively keeping the metal surface from rusting. The hexavalent chromium is a quite efficient rust proofing agent, but is highly toxic and adversely affects environment and human health. For this reason, there have been proposed a variety of methods for preventing rusting without using hexavalent chromium. For instance, Japanese Un-Examined Patent Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 52-92836 discloses a method for forming a conversion film on the surface of zinc and zinc alloys by treating the surface with an aqueous solution comprising titanium ions and at least one member selected from the group consisting of phosphoric acid, phytic acid, tannic acid and hydrogen peroxide and J.P. KOKAI No. Sho 57-145987 discloses a method for forming a conversion film on the surface of aluminum and aluminum alloys by treating the same with an aqueous solution comprising, as principal components, a silicate and a zinc compound. Japanese Patent Publication No. JP57145987 discloses a solution for chemical conversion coating treatment of aluminium or an aluminium alloy. The composition is a weakly acidic aqueous solution containing an oxidising agent, a vanadium compound or a titanium salt, a zinc compound and a water soluble silicate as essential components. European Patent Application EP0694593A discloses an anti-corrosive composition free from hexavalent chromium. The composition containing at least a polymer or copolymer in water solution or dispersion and at least a complex cation or anion containing a metal, and finally a strong oxidiser and acids to maintain the pH. International Application No. PCT/US94/08048 discloses a chromium free conversion coating comprising; (A) a component of specified anions; (B) a component of specified cations; the ratio of the total number of cations of this component of the total number of ions of component (A) being at least 1:5; (C) sufficient free acid to give the composition a pH in the range from 0.5 to 5.0; (D) a component selected from the group consisting of phosphorus containing inorganic oxyanions and phosphonate anions; and (E) a component selected from the group consisting of water soluble and water dispersable organic polymers and polymer resins. UK Patent Application No. GB2097024A discloses an aqueous acidic solution for treating zinc and zinc alloy surfaces containing effective amounts of (A) hydrogen ions to provide a pH of about 1.5 to about 2.2, (B) an oxidising agent, (C) at least one of a selected group of metal ions or mixtures thereof. However, these methods do not necessarily impart sufficient corrosion resistance practically acceptable to the metal surface and cannot supersede the treating methods using hexavalent chromium. Accordingly, the present invention provides a liquid rust proof film-forming composition capable of forming an excellent rust proof film on the surface of metal substrates, which composition is free of hexavalent chromium and preferably free of other chemical substances harmful to the environment. The present invention also provides a method for forming an excellent rust proof film on the surface of metal substrates. The present invention has been developed on the basis of such findings that an excellent rust proof film can be obtained by immersing a metal substrate in an aqueous solution comprising an oxidative substance, a silicate and/or silicon dioxide and specific metal ions and optionally oscillating or stirring the solution and that the corrosion resistance of the metal substrate can further be improved by applying an overcoat using, for instance, a colloidal silica-containing acrylic resin solution. According to a first aspect of the present invention, there is thus provided a liquid rust proof film-forming composition comprising (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, polyvalent carboxylic acids and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium and free of a water soluble or water dispersable polymer of copolymer having 0.5 to 8% of monomeric groups with chemical functions able to react with or to make compounds of metallic cations and which water soluble or water dispersable polymer or copolymer is stable at 40°C without precipitations, coagulations or gelations in the presence of phosphoric acid up to pH 1, or 6% of trichloride of hexahydrate chrome for two months and for 48 hours in the presence of hydrogen peroxide at 7.9%. According to a second aspect of the invention, there is provided a liquid rust proof film-forming composition comprising (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, malonic acid, succinic acid, maleic acid and diglycolic acid, and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium. According to yet another aspect of the invention, there is provided a method for forming a rust proof film on a metal substrate comprising the step of immersing the metal substrate in the liquid rust proof film-forming composition of the first or second aspect of the invention. According to another aspect of the present invention, there is also provided a method for forming a rust proof film which comprises the step of immersing a metal substrate in the foregoing liquid rust proof film-forming composition to form a rust proof film on the surface of the metal substrate. According to a further aspect of the present invention, there is provided a metal surface-treating method which comprises the steps of forming a rust proof film on a metal substrate by the aforementioned method and then overcoating the substrate with an inorganic or organic rust proof film. The present invention will hereinafter be described in detail with reference to the following preferred embodiments. Examples of the oxidative substances used in the liquid rust proof film-forming composition of the invention include peroxides and nitric acid. Specific examples of such peroxides include hydrogen peroxide, sodium peroxide and barium peroxide. Specific examples thereof usable herein also include peroxo acids and salts thereof such as performic acid, peracetic acid, perbenzoic acid, ammonium persulfate and sodium perborate. Among these, preferred is hydrogen peroxide and the use of 35% hydrogen peroxide is practically preferred. The overall concentration of the oxidative substance in the composition ranges from 0.001 to 3.0 mole/l and more preferably 0.01 to 1.0 mole/l. Examples of silicates used in the composition of the invention are alkali metal salts and ammonium salts such as lithium silicate, sodium silicate and potassium silicate, with sodium and potassium silicates being preferably used from the practical standpoint. Moreover, preferred silicon dioxide is colloidal silica. The concentration of the silicate and/or silicon dioxide preferably ranges from 0.001 to 2.0 mole/I and more preferably 0.05 to 1.0 mole/l. Examples of ionic species of metals usable in the present invention are Ti, Sr, Zr, V, and Wand any combination thereof. Specific examples of each ionic species are as follows. Examples of Ti ion sources are titanium salts such as titanium chloride and titanium sulfate, which may be used alone or in any combination. Examples of Zr ion sources are zirconyl salts such as zirconyl sulfate and zirconyl oxychloride; and zirconim salts such as Zr(SO 4 ) 2 and Zr(NO 3 ) 2 , which may be used alone or in any combination. Examples of Sr ion sources are strontium chloride, strontium fluoride, strontium peroxide and strontium-nitrate, which may be used alone or in any combination. Examples of V ion sources include vanadates such as ammonium vanadate and sodium vanadate; oxyvanadates such as vanadium oxysulfate; fluorides of vanadium and salts thereof such as vanadium fluoride, which may be used alone or in any combination. Examples of W ion sources include tungstates such as ammonium tungstate and sodium tungstate and mixture thereof. Ti ions are most preferably used in the composition of the invention among others. The total amount of these metal ions present therein preferably ranges from 0.0001 to 0.5 mole/l and more preferably 0.001 to 0.05 mole/l. In the present invention, the most preferred liquid rust proof film-forming composition is an aqueous solution comprising hydrogen peroxide, a silicate and a titanium compound which comprises metal cations of Ti and/or oxymetal anions thereof. The rust proof film-forming composition of the invention in general has a pH value falling within the range of from 0.5 to 6.0 and preferably 1.5 to 3.0. The pH value thereof can be adjusted by addition of an acid or an alkali. Specific examples of acids include mineral acids such as phosphoric acid, sulfuric acid, hydrochloric acid and nitric acid, while specific examples of alkalis are alkali metal hydroxides such as sodium and potassium hydroxides and aqueous ammonia. Moreover, the composition of the invention preferably comprises a chelating component capable of solubilizing metal ions in the composition. Examples of such chelating components are aliphatic amines such as ethylenediamine, diethylenetriamine and trimethyltetramine; aminoalcohols such as triethanolamine; aminocarboxylic acids such as EDTA, NTA, glycine and aspartic acid; hydroxycarboxylic acids such as glycolic acid, lactic acid, tartaric acid, malic acid, citric acid and tartrylgluconic acid; and polyvalent carboxylic acids such as malonic acid, succinic acid, maleic acid and diglycolic acid as well as alkali metal salts and ammonium salts thereof. These chelating agents may be used alone or in any combination. The kind and concentration of such chelating component are preferably selected while taking into consideration the kind and concentration of specific metal ions used. In particular, the overall concentration: C (mole/l) of the chelating components is preferably determined on the basis of the ratio thereof to the concentration: M (mole/l) of metal ions used and the ratio (C/M) is preferably not more than 50/1. If Ti ions are selected as the component (C) of the composition, the chelating agents preferably used are diglycolic acid, malonic acid or salts thereof. In addition, the conversion treatment solution of the present invention may comprise a nitrogen atom-containing compound for the stabilization of the silicate component present in the bath. Among the nitrogen atom-containing compounds, particularly preferred are carbonyl group-containing heterocyclic compounds such as N-methyl-2-pyrrolidone, ε-caprolactam, 1,3-dimethyl-2-imidazolidone, 2-pyrrolidone and caffeine. The content thereof in the treating solution preferably ranges from 0.01 to 0.1 mole/I. The balance of the liquid rust proof film-forming composition of the invention is preferably water. A rust proof film can be formed on the surface of a metal substrate by applying the foregoing liquid rust proof film-forming composition onto the metal substrate. Preferably, the subject to be treated is immersed in the treating solution. The temperature for treating the metal substrate surface with the composition is not restricted to a specific range, but preferably 20 to 50 °C from the practical standpoint. In addition, the treating time is not likewise limited to any specific range, but it desirably ranges from 5 to 180 seconds. The composition and method according to the present invention permit the formation of the foregoing rust proof film on any kind of metal substrate, but they are preferably applied to substrates of metals selected from the group consisting of Zn, Ni, Cu, Ag, Fe, Cd, Al, Mg and alloys thereof. In this respect, examples of such alloys include Zn-Ni alloys, Zn-Fe alloys, Zn-Sn alloys and Ni-P alloys, with metal substrate provided thereon with Zn and Zn alloy-plating films being most preferred in the present invention. The rust proof film to be formed is not limited in its thickness. In general, however, the thickness thereof is desirably on the order of from 0.01 to 1µm. According to the present invention, the foregoing rust proof film may further be overcoated with an inorganic or organic rust proof film. The overcoat used herein is not particularly restricted, but may be currently used inorganic or organic rust proof films such as those formed from colloidal silica, acrylic resins, silane coupling agents, silicates, epoxy resins and urethane resins, with those comprising water soluble acrylic resins, which contain 10 to 30% by weight of colloidal silica, being preferred from the practical point of view. Moreover, the metal substrate thus treated may further be subjected to coating treatments by, for instance, cationic electrodeposition, anionic electrodeposition or electrostatic spray coating, since such a coated film may also serve as surface preparation for paint and coating. Thus, the resulting substrate would further be improved in the corrosion resistance. As has been described above in detail, the composition and methods of the present invention permit the formation of an excellent rust proof film on the surface of metal substrates without using any chemical substance harmful to environment such as hexavalent chromium. The present invention will further be described in more detail with reference to the following working Examples and Comparative Examples. Example 1 A specimen was first prepared by applying a zinc or zinc alloy (an alloy comprising 30 to 99.5% by weight of zinc and 0.5 to 70% by weight of other components) plating film having a thickness ranging from 8 to 10µm onto the surface of an SPCC-polished steel plate (plate thickness: 0.3 mm; 100mm × 65mm). Then the specimen was immersed in each rust proof film-forming solution No. 1 to 6 according to the present invention specified in Table 1 at 25°C for 60 seconds followed by withdrawing the specimen, water-washing and drying the same. Each specimen which had been subjected to the foregoing treatment was subjected to the salt spray test according to JIS Z2371 for evaluating the corrosion resistance thereof. More specifically, the specimen was evaluated on the basis of the time required till the amount of white rust (the rate of the total area gathering white rust with respect to the total area of each specimen) exceeded 5%. The results thus obtained are summarized in the following Table 2. Salt Spray Test Results (5% white rust-forming time (hr)) Bath No. 1 2 3 4 5 6 (hr) 168 144 144 168 144 168 Comparative Example 1 The same specimen used in Example 1 was immersed in each comparative treating solution No. 7 to 10 specified in Table 3 at 25 °C for 60 seconds, followed by withdrawing, water-washing and drying the specimen. The specimens thus treated were inspected for the corrosion resistance by the same'method used in Example 1. The results obtained are summarized in the following Table 4. Comparative Treating Solution Bath Component (g/l) No.7 No. 8 No.9 No.10 Kind of Plating Zn Zn Zn Zn-Ni 35% H 2 O 2 50 2 -- 20 62% HNO 3 -- 2 -- -- potassium silicate 10 -- -- -- sodium silicate -- -- 50 -- 20% titanium chloride soln. -- 1 2 -- zirconium oxychloride -- -- -- 5 pH 2.0 2.0 1.8 2.5 (ph-adjusting agent) H 2 SO 4 H 2 SO 4 H 3 PO 4 H 2 SO 4 Bath No. 7 8 9 10 5% White Rust-Forming Time (hr) 6 24 3 6 Comparative Example 2 The same specimen used in Example 1 was subjected to a colorless chromate treatment, followed by withdrawing the specimen from the treating bath, water-washing and drying the same. The specimen thus treated was inspected for the corrosion resistance by the same method used in Example 1 and the 5% white rust-forming time thereof was found to be 168 hours. Example 2 An aluminum alloy (A1100) plate (plate thickness: 0.3 mm; 100mm x 65mm) was pre-treated in the usual manner, followed by immersing it in rust proof film-forming solution No. 3 as specified in Table 1 at 25 °C for 60 seconds and then water-washing and drying the same. The specimen thus treated was inspected for the corrosion resistance by the same method used in Example 1 and the 5% white rust-forming times thereof was found to be 48 hours Comparative Example 3 The same specimen used in Example 2 was immersed in the treating solution No. 7 or No. 9 used in Comparative Example 1 at 25°C for 60 seconds, followed by water-washing and drying the same. The specimens thus treated were inspected for the corrosion resistance by the same method used in Example 1 and the 5% white rust-forming times thereof were found to be 6 hours (for the treatment with the solution No. 7 ) and 6 hours (for the treatment with the solution No. 9 ), respectively. Example 3 A specimen which was prepared by applying a Zn plating film having a thickness of 8 to 10 µm onto an SPCC-polished steel plate (plate thickness: 0.3'mm; 100 mm× 65mm) was immersed in the rust proof film-forming solution No. 3 as specified in Table 1 at 25°C for 60 seconds, followed by withdrawing the specimen, water-washing and then applying a layer of "DIPCOAT W" (available from DIPSOL CHEMICALS CO., LTD.) as an organic resin overcoat. The specimen thus treated was inspected for the corrosion resistance by the same method used in Example 1. The result obtained is summarized in the following Table 5. Bath No. 3 DIPCOAT W Layer Applied Not Applied 5% White Rust-Forming Time (hr) 480 144 Comparative Example 4 To the same specimen used in Example 3, there was directly applied a layer of "DIPCOAT W" (available from DIPSOL CHEMICALS CO., LTD.) as an overcoat of a water-soluble organic resin. The specimen thus treated was inspected for the corrosion resistance by the same method used in Example 1 and the 5% white rust-forming time thereof was found to be 12 hours.

Claims: A liquid rust proof film-forming composition comprising (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, polyvalent carboxylic acids and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium and free of a water soluble or water dispersable polymer or copolymer having 0.5 to 8% of monomeric groups with chemical functions able to react with or to make compounds of metallic cations and which water soluble or water dispersable polymer or copolymer is stable at 40°C without precipitations, coagulations or gelations in the presence of phosphoric acid up to pH 1, or 6% of trichloride of hexahydrate chrome for two months and for 48 hours in the presence of hydrogen peroxide at 7.9%. A liquid rust proof film-forming composition comprising (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, malonic acid, succinic acid, maleic acid and diglycolic acid, and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium. A composition as claimed in claim 1 or 2 which comprises in the range of from 0.001 to 3.0 mole/l of the oxidative substance (A), from 0.001 to 2.0 mole/l of the silicate and/or silicon dioxide (B), and from 0.0001 to 0.5 mole/l of the metal ion component (C). A composition as claimed in any one of the preceding claims wherein the silicate is an alkali metal salt or ammonium salt of silicic acid. A composition as claimed in any one of the preceding claims wherein the silicon dioxide is colloidal silica. A composition as claimed in any one of the preceding claims wherein the pH ranges from 1.5 to 3.0. A composition as claimed in any one of the preceding claims wherein the oxidative substance is hydrogen peroxide. A composition as claimed in any one of the preceding claims wherein the chelating component is selected from ethylenediamine, diethylenetriamine, trimethyltetramine, triethanolamine, EDTA, NTA, glycine, aspartic acid, glycolic acid, lactic acid, tartaric acid, malic acid, citric acid, tartylgluconic acid, malonic acid, succinic acid, maleic acid and diglycolic acid and alkali metal salts and ammonium salts thereof. A composition as claimed in any one of the preceding claims additionally comprising a nitrogen atom-containing compound for the stabilization of the silicate component. A composition as claimed in claim 9 wherein the nitrogen atom-containing compound is also a carbonyl group-containing heterocyclic compound. A composition as claimed in claim 9 or claim 10 wherein the nitrogen atom-containing compound is selected from 2-methyl-2-pyrrolidone, ε-caprolactam, 1,3-dimethyl-2-imidazolidone, 2-pyrrolidone and caffeine. A method for forming a rust proof film on a metal substrate comprising the step of immersing the metal substrate in a liquid rust proof film-forming composition with comprises (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, polyvalent carboxylic acids and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium and free of a water soluble or water dispersable polymer or copolymer having 0.5 to 8% of monomeric groups with chemical functions able to react with or to make compounds of metallic cations and which water soluble or water dispersable polymer or copolymer is stable at 40°C without precipitations, coagulations or gelations in the presence of phosphoric acid up to pH 1, or 6% of trichloride of hexahydrate chrome for two months and for 48 hours in the presence of hydrogen peroxide at 7.9%. A method for forming a rust proof film on a metal substrate comprising the step of immersing the metal substrate in a liquid rust proof film-forming composition with comprises (A) from 0.001 to 3.0 mole/l of an oxidative substance selected from the group consisting of peroxides and nitric acid, (B) a silicate and/or silicon dioxide, (C) at least one member selected from the group consisting of metal cations of Ti, Zr, Sr, V and W, and oxymetal anions thereof, (D) at least one chelating component selected from aliphatic amines, aminoalcohols, aminocarboxylic acids, hydroxycarboxylic acids, maleic acid, succinic acid, malonic acid and diglycolic acid; and alkali metal salts and ammonium salts thereof which is capable of solubilizing the metal ions in the liquid rust proof film-forming composition and (E) water, the composition having a pH of from 0.5 to 6, the composition being free of hexavalent chromium. A method as claimed in claim 12 or 13 wherein the metal substrate is immersed in the liquid rust proof film-forming composition at a temperature in the range of from 20 to 50°C for from 5 to 180 seconds. A method as claimed in any one of claims 12 to 14, further comprising the step of overcoating the resulting substrate having a rust proof film thereon with an inorganic or organic rust proof film.

Inventors: INOUE MANABU, OHNUMA TADAHIRO, SATO GO, YAMAMOTO TOMITAKA, INOUE, MANABU, OHNUMA, TADAHIRO, SATO, GO, YAMAMOTO,TOMITAKA, Inoue, Manabu, Techn.Ctr., Dipsol Chem. Co., Ltd., Ohnuma, Tadahiro, Techn.Ctr., Dipsol Chem.Co.,Ltd., Sato, Go, Techn.Ctr., Dipsol Chem. Co., Ltd., Yamamoto,Tomitaka, Techn.Ctr., Dipsol Chem.Co.,Ltd
Applicants: DIPSOL CHEM, DIPSOL CHEMICALS CO., LTD.
Application year: 1996
Main classification: C23C22
IPC codes: C23C22, C23F11, C09D5