Patent Application
20060261311
The present invention sets out to develop an anticorrosion coating for metal parts, preferably free of hexavalent chromium, that has improved anticorrosion properties.
The present invention applies to all types of metal parts, in particular in steel or cast iron or whose surface is formed of a layer of zinc or zinc alloy, which require high resistance to corrosion, on account of their intended use in the automotive industry for example. Anticorrosion coating compositions, free of hexavalent chromium, have already been recommended. Some of these compositions contain a particulate metal. The particulate metal, such as zinc and/or aluminium, is in suspension in the composition and provides the metal part with sacrificial protection against a corrosive medium. Aqueous anticorrosion coating compositions for example have been described for metal parts, containing a particulate metal, an appropriate solvent, a thickener and a binder formed of a silane. Particulate metal-based compositions have also been described whose storage stability and anticorrosion performance are improved through the incorporation of molybdenum oxide (MoO3) in the composition.
Within the scope of the present invention, the applicant has discovered that it is possible to improve the anticorrosion properties of compositions containing particulate metal by incorporating therein at least one element chosen from among yttrium, zirconium, lanthanum, cerium, praseodymium and neodymium, in the form of oxides or salts.
The anticorrosion performance of coating compositions containing particulate metal prove to be further improved when the above-cited elements are associated with molybdenum oxide.
The compositions containing particulate metal concerned, by the present invention may be aqueous phase or organic phase compositions. They are recommended when high resistance to corrosion is required.
The subject of the present invention is therefore the use of at least one element chosen from among yttrium, zirconium, lanthanum, cerium, praseodymium and neodymium in the form of oxides or salts, as agent to reinforce the anticorrosion properties of an anticorrosion coating composition containing a particulate metal, in aqueous or organic phase, for metal parts.
A further subject of the invention is the use of at least one of the above-cited elements, optionally associated with molybdenum oxide MoO3, as reinforcing agent for the anticorrosion properties of an anticorrosion coating composition containing a particulate metal, in aqueous or organic phase, for metal parts.
Without this interpretation being restrictive, it would seem that the presence of at least one of the above-cited elements makes it possible to reinforce the efficacy of the anticorrosion protection imparted by the particulate metal in the composition.
The particulate metal present in the composition is preferably added in powder form, of different geometric, homogeneous or heterogeneous structures, in particular spherical, laminar, lenticular forms or other specific forms.
The oxides or salts of the above-cited elements which are used as reinforcing agents for the anticorrosion properties of the composition, are generally in powder form whose particles have a D50 of less than 20 μm (the value D50 means that 50% by number of the particles have a particle size of less than this value, and 50% by number of the particles have a particle size greater than this value). During the preparation of the coating composition, a prior particle grinding or dispersion step (to break up agglomerates into elementary particles) may be conducted so that the composition contains particles with a D50 of less than 3 μm.
These oxides or salts may be fully soluble, partially soluble or completely insoluble in aqueous phase or organic phase. They may be in dispersed or solubilised form within the composition.
Yttrium salts are advantageously chosen from among yttrium acetate, chloride, formate, carbonate, sulfamate, lactate, nitrate, oxalate, sulfate, phosphate and aluminate (Y3Al5O12), and their mixtures.
Yttrium oxide is advantageously in the form Y2O3.
Yttrium is preferably used in oxide form.
The yttrium oxide Y2O3 used to prepare the coating composition is generally in the form of particles having a size of between 1 μm and 40 μm, with a D50 of approximately 6 to 8 μm. When preparing the coating composition, a prior particle grinding or dispersion step (to break up agglomerates into elementary particles) may be conducted so that the composition contains particles having a D50 of less than 3 μm.
Zirconium salts are preferably chosen from among zirconium carbonate, silicate, sulfate, and titanate, and their mixtures.
Zirconium oxide is advantageously in the form ZrO2.
Lanthanum salts are advantageously chosen from among lanthanum acetate, oxalate, nitrate, sulfate, carbonate, phosphate and aluminate (LaAlO3), and their mixtures.
Lanthanum oxide is preferably in the form La2O3.
Cerium salts are advantageously chosen from among cerium chloride, carbonate, acetate, nitrate, oxalate, sulfate, phosphate, molybdate (Ce2(MoO4)3) and tungstate (Ce2(WO4)3), and their mixtures.
Cerium oxide is advantageously in the form CeO2.
Cerium is preferably used in the form of cerium chloride or CeO2.
Praseodymium salts are advantageously chosen from among praseodymium carbonate, chloride, nitrate, oxalate and sulfate, and their mixtures.
Praseodymium oxide is advantageously in the form Pr6O11.
Neodymium salts are advantageously chosen from among neodymium carbonate, chloride, nitrate and sulfate, and their mixtures.
Neodymium oxide is advantageously in the form Nd2O3.
When the composition also contains molybdenum oxide MoO3 associated with one of the above-cited elements used as reinforcing agent for the anticorrosion properties of the composition, MoO3 is advantageously incorporated in essentially pure orthorhombic crystalline form, having a molybdenum content of more than around 60% by weight.
Preferably, the molybdenum oxide MoO3 is in the form of particles having a size of between 1 μm and 200 μm.
Preferably, said reinforcing agent for the anticorrosion properties of the composition is associated with molybdenum oxide MoO3 in a weight ratio of 0.25<anticorrosion property reinforcing agent: MoO3<20, preferably 0.5<anticorrosion property reinforcing agent:MoO3<16, further preferably 0.5<anticorrosion property reinforcing agent:MoO3<14.
Preferably yttrium oxide Y2O3 is used in association with molybdenum oxide MoO3. A further subject of the invention is the use of yttrium oxide Y2O3 in association with molybdenum oxide MoO3 in a weight ratio of 0.25<Y2O3:MoO3<20, preferably 0.5<Y2O3:MoO3<16, further preferably 0.5<Y2O3:MoO3<14.
A further subject of the invention concerns anticorrosion coating compositions for metal parts, comprising:
The coating composition contains at least one particulate metal, i.e. one or more particulate metals.
Advantageously, the particulate metal content lies between 10% and 40% by weight relative to the weight of the composition.
The particulate metal may be chosen from among zinc, aluminium, tin, manganese, nickel, their alloys, and their mixtures.
Preferably the particulate metal is chosen from among zinc, aluminium, their alloys and their mixtures. Preferably the alloys are chosen from the alloys of zinc and aluminium containing at least 3% by weight aluminium, preferably 7% by weight of aluminium, and the zinc and tin alloys containing at least 10% by weight of tin.
The content of anticorrosion property reinforcing agent of the composition preferably lies between 0.5% and 10% by weight relative to the weight of the composition, preferably between 1% and 8% by weight relative to the weight of the composition, further preferably between 1% and 7% by weight relative to the weight of the composition.
The reinforcing agent for the anticorrosion properties of the composition is advantageously yttrium, preferably in the oxide form Y2O3, or cerium preferably in the form of cerium chloride.
The reinforcing agent for the anticorrosion properties of the composition is advantageously associated with molybdenum oxide MoO3 in a weight ratio of 0.25<anticorrosion property reinforcing agent:MoO3<20, preferably 0.5<anticorrosion property reinforcing agent:MoO3<16, further preferably 0.5<anticorrosion property reinforcing agent:MoO3<14.
The binder content preferably lies between 3% and 20% by weight relative to the weight of the composition. The binder may be of organic and/or mineral type in aqueous or organic phase. The choice of the binder depends on different criteria, among which is the baking temperature of the coating composition.
The binder is preferably chosen from among an alcoxylated silane, optionally organofunctionalised, such as γ-glycidoxypropyltrimethoxysilane or γ-glycidoxy-propyltrimethoxysilane, a silicone resin, a silicate of sodium and/or potassium and/or lithium, a zirconate, a titanate, an epoxy resin, a phenoxy resin, an acrylic and their mixtures.
The binder may be associated with a crosslinking agent of phenolic type,aminoplast type, or dicyandiamide type. Acid catalysts may also be added in order to catalyse the crosslinking reaction.
If the composition is in aqueous phase, a colloidal silica may be used in association with resins, as binder.
If the coating composition is in aqueous phase, the liquid phase is formed of water and may also contain up to 30% by weight of an organic solvent or a mixture of organic water-miscible solvents.
If the coating composition is in organic phase, the liquid phase is entirely made up of an organic solvent or a mixture of organic solvents miscible inter se.
The organic solvent or solvents are chosen in relation to the binder, so as to solubilise the latter or stabilise a dispersion thereof. The organic solvent or solvents are advantageously chosen from white spirit, alcohols, ketones, aromatic solvents and glycol solvents such as glycol ethers, in particular diethyleneglycol, triethyleneglycol and dipropyleneglycol, acetates, polyethyleneglycol and nitropropane, and their mixtures.
The coating composition may also contain a thickener if the type of application so requires, if it is to be applied by dipping-centrifuging for example.
The content of thickening agent is advantageously less than 7% by weight relative to the weight of the composition, preferably between 0.005% and 7% by weight relative to the weight of the composition.
The thickening agent is advantageously chosen from among the cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxy-propylcellulose or hydroxypropylmethylcellulose, xanthane gum, associative thickeners of polyurethane or acrylic type, silicas, silicates such as silicates of magnesium and/or lithium optionally treated, or organophilic clays, and their mixtures.
The coating composition may also comprise a lubricating agent in sufficient quantity to obtain a self-lubricated system, chosen in particular from among polyethylene, polytetrafluoroethylene, MoS2, graphite, polysulfones, synthetic or natural waxes and nitrides, and their mixtures.
If it is in aqueous phase, the coating composition may also contain other additives compatible with the binder, chosen from among an anti-foam agent such as Schwego foam (emulsified hydrocarbon) from Schwegrnan, a wetting agent such as an ethoxylated monylphenol or an ethoxylated polyalcohol, a surfactant agent such as Aerosol TR 70 (sodium sulfosuccinate) from Cytec, and a biocide such as Ecocide D75 from Progiva, and a weak acid such as boric acid to adjust the pH of the composition.
In preferred manner, the coating composition contains the following ingredients:
If the above-cited anticorrosion property reinforcing agent is associated with molybdenum oxide, the latter preferably represents 0.5% to 2% by weight of the composition.
Evidently, the present invention also extends to anticorrosion coatings applied to metal parts using the above-cited compositions.
Application may be made by spraying, dipping-draining or dipping-centrifuging, the layer of coating then being subjected to a baking operation (by convection or infrared for example) preferably conducted at a temperature of between 70° C. and 350° C., for approximately 10 to 60 minutes, by convection.
According to one advantageous embodiment, the anticorrosion coating derives from an application operation involving, prior to the baking operation, a drying operation of the coated metal parts (by convection, or infrared for example), in particular by convection at a temperature in the region of 70° C. for approximately 10 to 30 minutes on line.
Under these conditions, the thickness of the dry film so applied lies between 3 μm (11 g/m2) and 15 μm (55 g/m2), preferably between 4 μm (15 g/m2) and 10 μm (40 g/m2), further preferably between 5 μm (18 g/m2) and 10 μm (40 g/m2).
The present invention also extends to the metal substrate, preferably in steel, provided with an anticorrosion coating applied using the above-cited compositions.
This itself may be coated with another coating to further reinforce some properties, such as anticorrosion protection or lubrication. A coating to reinforce the anticorrosion protection may contain an alkaline silicate, in particular a sodium and/or potassium and/or lithium silicate, an acrylic, a zirconate, a titanate, a silane, an epoxy resin, a phenol resin or one of their mixtures, these resins optionally being associated with a colloidal silica. A coating for lubrication may contain a lubricating agent chosen from among polyethylene, polytetrafluoroethylene, MoS2, graphite, polysulfones, synthetic or natural waxes, and nitrides, and their mixtures.
Corrosion Tests
A) Influence of Yttrium Oxide (Y2O3) in Aqueous Phase Optionally Associated with Molybdenum Oxide (MoO3) on Anticorrosion Performance.
Comparative experiments were conducted on the coating compositions given in table 1.
1 Y2O3 of 99.99% purity (Rhodia)
2 Zinc in paste form, approx. 92% in white spirit (80% Alu Stapa PG Chromal VIII, from Eckart Werke)
3 Aluminium, approx. 80% in dipropylene glycol
4 γ-glycidoxypropyltrimethoxysilane (Crompton)
5 Sodium silicate (Rhodia)
6 Wetting agent of ethoxylated nonylphenol type (Uniqema)
7 Wetting agent of ethoxylated nonylphenol type (Uniqema)
8 Anti-sedimentation agent of silica type (Degussa)
9 Antifoam of hydrocarbon type.
Prepared samples
The steel screws treated in this manner were tested with salt spray according to standard NFISO 9227. Results of salt spray resistance are given in table 2.
Table 2 clearly shows that the addition of yttrium oxide Y2O3 to coating compositions increases resistance to salt spray in samples treated with these compositions.
Also, when yttrium oxide Y2O3 is associated with molybdenum oxide MoO3, the anticorrosion performance is further improved. An interaction is observed or a synergy effect between Y2O3 and MoO3, which increases the composition's anticorrosion performance.
B) Influence of Zinc Allowed with 7% Aluminium (Stapa Zn4Al7, from Eckkart Werke) on Anticorrosion Performance.
Comparative experiments were conducted on the coating compositions listed in table 3.
Prepared samples:
The steel screws were treated with the coating compositions in table 3, then tested with salt spray according to standard NFISO 9227.
Results of resistance to salt spray are given in table 4.
Table 4 shows that the anticorrosion performance of the composition is better with alloyed zinc than with zinc.
C) Influence of Cerium Chloride in Aqueous Phase on Anticorrosion Performance
Comparative experiments were conducted on the coating compositions listed in table 5.
Prepared samples
The steel screws were treated with the coating compositions in table 5, then tested with salt spray in accordance with standard NFISO 9227.
The results of resistance to salt spray are given in table 6.
Table 6 clearly shows that the addition of cerium chloride to coating compositions increases the resistance to salt spray of the samples treated with these compositions.
D) Influence of Yttrium Carbonate in Aqueous Phase on Anticorrosion Performance
Comparative experiments were conducted on the coating compositions listed in table 7.
Steel screws were prepared, treated and tested as in example 1. Results of salt spray resistance are given in table 8.
Table 8 clearly shows that, when yttrium carbonate is associated with molybdenum oxide MoO3, the anticorrosion performance is improved. An interaction is observed or a synergy effect between yttrium carbonate and MoO3, which increases the composition's anticorrosion performance.
E) Influence of Various Oxides in Aqueous Phase on Anticorrosion Performance
Comparative experiments were conducted on the coating compositions listed in table 9.
E-1) Electrochemistry
Polarisation resistance of the coatings was measured during one hour with SOLARTRON 1250 analyzer (Schlumberger), air exposed, with a scanning rate of ±10 mV at 0.1 mV.s−1. Results of these measurements are given in table 10. The higher the value of polarization resistance, the better the anticorrosion performance of the coatings is expected.
Table 10 clearly shows that the addition of oxide of yttrium, cerium, lanthanum, praseodymium, neodymium or zirconium to coating compositions increases the polarization resistance of coatings, which indicates that the corrosion resistance of the coating will be likely increased.
E-2) Corrision Resistance
Steel screws were prepared, treated and tested as in example 1. Results of salt spray resistance are given in table 11.
Table 11 clearly shows that the addition of oxide of yttrium, lanthanum, praseodymium, neodymium or zirconium to coating compositions increases the resistance to salt spray of the samples treated with these compositions. The best oxide appears to be Y2O3, but Neodynium, Praseodynium and Lanthanum give also very good results too.
Furthermore, when the oxide is associated with molybdenum oxide MoO3, the anticorrosion performance is further improved. An interaction is observed or a synergy effect between the oxide and MoO3, which increases the composition's anticorrosion performance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0308596 | Jul 2003 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB04/02450 | 7/13/2004 | WO | 1/13/2006 |
