WO2019157612A1 - Surface treatment composition for light metallic material - Google Patents

Surface treatment composition for light metallic material Download PDF

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Publication number
WO2019157612A1
WO2019157612A1 PCT/CN2018/076596 CN2018076596W WO2019157612A1 WO 2019157612 A1 WO2019157612 A1 WO 2019157612A1 CN 2018076596 W CN2018076596 W CN 2018076596W WO 2019157612 A1 WO2019157612 A1 WO 2019157612A1
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WIPO (PCT)
Prior art keywords
surface treatment
metallic material
acid
treatment composition
light metallic
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PCT/CN2018/076596
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French (fr)
Inventor
Wenzhang WU
Xing Wang
Junjun Wu
Huimin Cao
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Henkel Ag & Co. Kgaa
Henkel (China) Co., Ltd.
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Priority to PCT/CN2018/076596 priority Critical patent/WO2019157612A1/en
Publication of WO2019157612A1 publication Critical patent/WO2019157612A1/en

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/57—Treatment of magnesium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/56—Treatment of aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
    • C23C22/08—Orthophosphates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
    • C23C2222/20—Use of solutions containing silanes

Definitions

  • This invention relates to a surface treatment composition for light metallic material.
  • the present invention relates to a surface treatment composition for light metal and its alloy and a transparent conversion coating thereof conferring to an excellent corrosion resistance and a reliable adhesion.
  • light metal materials such as aluminium and magnesium materials are the lightest ones and also have high specific strength and therefore, they have been applied in various fields such as interior and exterior parts for motor cars and two-wheeled vehicles, parts for household appliances, containers for storage such as bags and suitcases, goods for sports, parts for optical machinery and tools, sticks and further new fields in electronic industries such as computers and acoustics.
  • the light metal materials, especially the magnesium materials are the most active metal materials and accordingly, it has been difficult to use them per se without any treatment because of their low corrosion resistance.
  • conversion coatings in general, is a well-known method of providing light metals and their alloys with one or more layers or coatings that impart increased corrosion resistance and adhesion of subsequently applied finishes/coatings (i.e., lacquer, enamel, vanish, shellac, topcoat, and the like) to the metals.
  • the surface of the articles cannot be subjected to painting.
  • the surface of the magnesium material is highly susceptible to oxidation and therefore, the article should be subjected to any surface treatment to maintain the initial gloss and color tone of the metal substrate surface thereof.
  • the coating obtained through the conventional chemical conversion treatment or anodization treatment using chromic acid or a bichromate gets colored.
  • such treatments will produce hexavalent chromium ion in waste liquid, which does not meet the requirement of environment protection. Therefore, it is necessary to find a surface treatment solution free of hexavalent chromium ion for light metal materials to achieve corrosion resistance, adhesiveness and gloss and color tone as desired.
  • US 7695771 B2 discloses a process for forming a non-chromate conversion coating on surfaces of magnesium or magnesium alloys by using a process solution which is an acidic aqueous solution comprising at least one fluorosilicon acid, optionally, at least one water-soluble pH adjustment agent, optionally, at least one surfactant and optionally, aluminum as cations or as at least one compound or any combination of these.
  • a process solution which is an acidic aqueous solution comprising at least one fluorosilicon acid, optionally, at least one water-soluble pH adjustment agent, optionally, at least one surfactant and optionally, aluminum as cations or as at least one compound or any combination of these.
  • the conversion coating disclosed in the patent is colorful and well-visible.
  • US 7819989 B2 discloses a composition for surface treatment of aluminum, an aluminum alloy, magnesium or a magnesium alloy comprising: (1) compound A containing at least one metal element selected from the group consisting of Hf (IV) , Ti (IV) and Zr (IV) , (2) fluorine-containing compound of a sufficient amount to make fluorine exist in the composition in an amount of at least 5 times the molarity of the total molarity of the metal contained in the above-mentioned compound A, (3) at least one metal ion B selected from the group of alkaline earth metals, (4) at least one metal ion C selected from the group consisting of Al, Zn, Mg, Mn and Cu, and (5) nitric ion.
  • the surface treatment composition will produce fluoride ion in waste liquid, which is not friendly to environment.
  • US 6773516 B2 discloses an aqueous acidic solution for forming a rare earth element containing conversion coating on the surface of a metal, said solution being substantially chromate-free and including effective quantities of at least one cerium (III) containing species, an oxidant and at least one accelerator comprising a metal selected from Sb, Bi, Te, and Se.
  • the conversion coating thus produced is in yellow color.
  • US 6200693 B2 discloses an aqueous liquid composition for treating the surfaces of light metals and light metal alloys, said liquid composition having a pH value within a range from 1.0 to 7.0 and consisting essentially of water and the following components: (A) from 0.01 to 50 g/L of a component selected from the group consisting of permanganic acid, water soluble salts thereof, and mixtures of any two or more of permanganic acid and any of its water soluble salts; and (B) from 0.01 to 20 g/L of a component selected from the group consisting of water soluble compounds of titanium, water soluble compounds of zirconium, and mixtures of any two or more of said water soluble compounds of titanium and zirconium.
  • the conversion coating thus produced may be colorful due to the use of permanganic acid in the composition.
  • US 9290846 B2 relates to a composition for surface treatment of aluminum alloys, comprising a conducting polymer dispersion (such as polypyrrole) , at least one silane and inorganic metallic salts, wherein a pH of the composition is between 1.0 and 6.0, and wherein the inorganic metallic salts comprise at least one zirconium salt and at least one cerium nitrate salt, but the color of the resulting conversion coating depends upon the metallic surface and the bath/spray parameters.
  • a conducting polymer dispersion such as polypyrrole
  • silane silane
  • inorganic metallic salts comprise at least one zirconium salt and at least one cerium nitrate salt
  • US 8609755 B2 relates to a storage stable composition for treating metal surfaces such as aluminum, consisting essentially of: a) an aqueous solution of partial and/or complete condensate of ureidosilane, b) a stabilizing agent selected from the group consisting of alcohols, glycols, triol, polyols, glycol ethers, esters, ketones, pyrolidones and polyether silanes; and c) a colloidal cerium oxide.
  • CN 102115880 A teaches a surface treatment composition for light metal or its alloy comprising a titanium containing compound, a vanadium containing compound and an organic acid, wherein the organic acid contains 1 to 100 carbon atoms and 2 to 50 oxygen atoms.
  • WO 2016044972 A1 discloses an alkaline aqueous composition for the pretreatment of metal substrates such as aluminum alloy, comprising a source of cerium cations and an amino-functional organosilane.
  • the present invention provided the surface treatment composition and its solution for light metal or its alloy as well as the surface treatment method which overcome the abovementioned disadvantage of present hexavalent chromium ion free surface treatment method of light metal materials.
  • the surface treatment composition in this invention is free of hexavalent chromium ion and could significantly improve the corrosion resistance of light metal and its alloy.
  • the surface treatment solution in this invention is stable and transparent. Besides, the surface treatment method in this invention is simple and suitable for industrial production.
  • the present invention in general, provides a surface treatment composition for light metallic material, especially light metallic material, comprising:
  • the present invention also provides an aqueous surface treatment solution for light metallic material, comprising the surface treatment composition for light metallic material according to the present invention and water, a conversion coating prepared by the surface treatment composition or the aqueous surface treatment solution for light metallic material, and an article of manufacture, comprising a conversion coating prepared by the surface treatment composition for light metallic material.
  • the present invention provides a method for improving corrosion resistance of a metallic substrate, comprising:
  • Figure 1 illustrates the appearance of a coated magnesium alloy substrate treated by the working solution of Example 1.
  • Figure 2 illustrates the test result of a coated magnesium alloy substrate treated by the working solution of Example 1 and having a top coat according to ASTM D3359.
  • the surface treatment composition for light metallic material comprises a rare earth element containing compound.
  • the rare earth element containing compound is a compound containing yttrium, lanthanum and/or cerium, and preferably is a cerium containing compound in view of cost-efficiency.
  • the rare earth element containing compound is a water-soluble compound so as to be further formulated as aqueous solution.
  • water-soluble used herein it means that more than 5g/L of rare earth element containing compound can be dissolved into deionized water at 20 °C while still a homogenous solution is attained without visible precipitates over a period of 24 h.
  • the cerium containing compounds in the present invention may be selected from tetravalent cerium compounds, trivalent cerium compounds, and/or hydrate of the same.
  • Lanthanide ions as cerium (III) and cerium (IV) forming insoluble hydroxides show low toxicity and are economically competitive products, since cerium is relatively abundant in nature. Therefore, tetravalent and trivalent cerium compounds have been investigated to develop corrosion protection systems for light metallic materials as alternative to chromates.
  • tetravalent and trivalent cerium compounds include cerium (IV) hexanitrates such as cerium (IV) diammonium nitrate and potassium cerium (IV) nitrate; cerium (IV) tetraammonium sulfate; and cerium (IV) sulfate.
  • the cerium compounds may be hydrates such as cerium (IV) tetraammonium sulfate dihydrate, and cerium (IV) sulfate tetrahydrate. Two or more of the tetravalent cerium compounds may be used in combination.
  • the trivalent cerium containing compound used in the present invention may be any one of cerium (III) acetate, cerium (III) ammonium nitrate, cerium (III) carbonate, cerium (III) chloride, cerium (III) fluoride, cerium (III) nitrate, cerium (III) sulfate, cerium (III) bromide, cerium (III) iodide, cerium (III) oxalate, cerium (III) perchloride, cerium (III) sulfide, and hydrates of the same. Two or more of the foregoing trivalent cerium compounds may be used in combination.
  • the tetravalent cerium compound (s) and the trivalent cerium compound (s) may be used singly or in combination.
  • the cerium containing compounds are trivalent cerium containing compound, and more preferably is selected from cerium (III) acetate, cerium (III) ammonium nitrate, cerium (III) carbonate, cerium (III) nitrate, hydrates of the same and mixture thereof.
  • the surface treatment composition for light metallic material in the present invention also comprises a silane coupling agent. It is known in the art that silane coupling agents can be added in the surface treatment compositions for light metallic materials to improve the adhesiveness of the coating formed on the metal surface.
  • silane coupling agents to be used in the surface treatment compositions, as long as the silane coupling agents are compatible to the rare earth element containing compound, such as the water-soluble cerium salts and other components contained in the surface treatment composition.
  • the silane coupling agents may have an amino functional group or epoxy functional group.
  • the amino or epoxy functional silane may comprise C 2 -C 10 -alkoxy-groups.
  • the silane coupling agent may have the general structure R 1 -Si-X 3 , where R 1 is a reactive organofunctional group and at least one of X is a hydrolysable group and others are optionally substituted alkyl or an aryl group containing 1 to 10 carbon atoms.
  • the hydrolysable group may be selected from alkoxy, acyloxy, halogen or amine.
  • the alkoxy may be a C 1 -C 6 alkoxy (e.g. a methoxy or ethoxy group) ;
  • the acyloxy may be a phenyloxy, and;
  • the halogen may be may be a chloride or a bromide.
  • R 1 may be an optionally substituted alkyl or an aryl group containing 1-10 carbon atoms, e.g. 2-10 carbon atoms. If R 3 is a substituted alkyl or an aryl group containing 1-10 carbon atoms, R 1 is preferably substituted with one or more amine or epoxy functional groups. In these cases, the silane coupling agent may then be described as an amino functional silane or an epoxy functional silane respectfully.
  • Some exemplary epoxy functional silanes include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane or beta- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane.
  • R 3 is an alkyl or an aryl group containing 1 to 10 carbon atoms substituted with one or more amine groups, or an aryl group (e.g. phenyl group) containing 5 to 10 carbon atoms substituted with one or more amine groups.
  • the amine groups may be one or more primary, secondary or tertiary amine groups.
  • a suitable amine functional silane coupling agent for use in the surface treatment composition of the present invention has the structure: (R 2 -O) 3 -Si-R 3 -NH 2 , wherein R 2 is an alkyl group containing 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms and most preferably is a methyl group, R 3 is an alkylene moiety containing 1 to 10 carbon atoms optionally substituted with an amine group.
  • amine functional silane coupling agent examples include aminomethylaminopropyltrimethoxylsilane (MeO) 3 -Si- (CH 2 ) 3 -NH- (CH 2 ) -NH 2 ) , aminopropyltrimethoxysilane ( (MeO) 3 -Si- (CH 2 ) 3 -NH 2 ) , and/or aminopropyltriethoxysilane ( (EtO) 3 -Si- (CH 2 ) 3 -NH 2 ) .
  • silane coupling agents suitable for the present invention include but not limited to 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, 3- [2- (2-aminoethylamino) ethylamino] propyltrimethoxysilane, N- (2-aminoethyl) -3-aminoisobutylmethyldimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-
  • the amine functional silane coupling agent and/or epoxy functional silane coupling agent can be singly used or in combination.
  • the surface treatment compositions for light metallic material according to the present invention also comprises a polyhydroxyl monocarboxylic acid.
  • polyhydroxyl monocarboxylic acid used herein should be understood in a broad sense, and it refers to a source of an organic acid having one carboxylic group and two or more hydroxyl groups, preferably from 2 to 6 hydroxyl groups including free acid form and lactone form, but not including salt form.
  • the salt of polyhydroxyl monocarboxylic acid may be further added in the surface treatment composition, in combination with the free acid form and/or lactone form of polyhydroxyl monocarboxylic acid.
  • the lactone of a polyhydroxyl monocarboxylic acid transforms to free acid when it dissolves in solvent such as water.
  • the polyhydroxyl monocarboxylic acid may exist as stereoisomers as D, L, and DL forms.
  • the polyhydroxyl monocarboxylic acid has the structure represented by
  • R 4 is alkyl, alkoxyl, aralkyl, or aryl group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH
  • R 5 and R 6 are each independently alkylene, alkoxylene, aralkylene or arylene group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH, with the proviso that the number of hydroxyl groups in R 4 , R 5 and R 6 is two or more, and preferably from 2 to 6.
  • R 6 is hydroxymethylene, and the polyhydroxyl monocarboxylic acid is an ⁇ -hydroxyl acid having one carboxyl group and two or more hydroxyl groups.
  • R 4 is linear alkyl or alkoxyl optionally substituted by OH, and preferably is linear alkyl optionally substituted by OH
  • R 5 and R 6 are each independently linear alkylene or alkoxylene optionally substituted by OH, and preferably is linear alkylene optionally substituted by OH.
  • R 4 , R 5 and R 6 are all saturated groups.
  • R 4 , R 5 and R 6 have 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms in total.
  • the examples of such polyhydroxyl monocarboxylic acid include but not limited to 2, 3-dihydroxypropanoic acid, 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, 2, 3, 4, 5, 6, 7-hexahydroxyheptanoic acid, 2, 3, 4, 5, 6, 7, 8-hexahydroxyoctanoic acid, 2, 3-dihydrobutanoic acid, 2, 4-dihydrobutanoic acid, 2, 3-dihydropentanoic acid, 2, 4-dihydropentanoic acid, 2, 5-dihydropentanoic acid, 2, 3, 4-trihydropentanoic acid, 2, 3, 5-trihydropentanoic acid, 2, 4, 5-trihydropentanoic acid, 2, 3-dihydroxyhexanoic acid, 2, 4-dihydroxyhexanoic acid, 2, 5-dihydroxyhexanoic acid, 2, 6-dihydroxyhexanoic acid, 2,
  • the polyhydroxyl monocarboxylic acid has a linear and saturated carbon chain containing 4 to 8 carbon atoms, such as 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, 2, 3, 4, 5, 6, 7-hexahydroxyheptanoic acid, 2, 3, 4, 5, 6, 7, 8-hexahydroxyoctanoic acid, and lactone, isomer, derivative, and mixture thereof.
  • 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, and lactone isomer, derivative, and mixture thereof.
  • polyhydroxyl monocarboxylic acids suitable for the present invention includes 2, 3-dihydroxy-2-methylbutyric acid, 2-methylglyceric acid, glyceric acid, 2- (hydroxymethyl) -3-hydroxypropionic acid, 2, 2- (dihydroxymethyl) propionic acid, 2, 3-dihydroxyisovaleric acid, 2, 3-dihydroxy-3-methylbutyric acid, 2-hydroxymethyl-4-hydroxybutanoic acid, 2, 4-dihydroxy-3, 3-dimethylbutanoic acid, 2, 3-dihydroxy-3-methylpentanoic acid, 2, 4-dihydroxy-3-methylpentanoic acid, 2, 5-dihydroxy-3-methylpentanoic acid, 3, 5-dihydroxy-3-methylpentanoic acid, 2, 2-bis (hydroxymethyl) butanoic acid, 3, 5-dihydroxy-2, 3-dimethylpentanoic acid, 3, 5-dihydroxy-3, 4-dimethylpentanoic acid, 2, 4-dihydroxy-2, 4-dimethylpentanoic acid, 2- (1
  • the polyhydroxyl monocarboxylic acids can be singly used or in combination.
  • the polyhydroxyl monocarboxylic acid is selected from 2, 3, 4, 5, 6-pentahydroxyhexanoic acid (such as D-gluconic acid) , lactone of 2, 3, 4, 5, 6-pentahydroxyhexanoic acid (such as D- gluconolactone) , 2, 3, 4-trihydroxybutanoic acid (such as D-erythronic acid) , lactone of 2, 3, 4-trihydroxybutanoic acid (such as D-erythronolactone) , and mixture thereof.
  • the polyhydroxyl monocarboxylic acid may be used with it salts in combination, and in one embodiment, the surface treatment composition according to the present invention further comprises a salt, preferably a water-soluble salt, of polyhydroxyl monocarboxylic acid, such as alkali metal salt (e.g. salt of sodium, potassium or lithium) , alkali earth metal salt (e.g. magnesium salt) , aluminum salt, zinc salt, and ammonium salt of polyhydroxyl monocarboxylic acid.
  • alkali metal salt e.g. salt of sodium, potassium or lithium
  • alkali earth metal salt e.g. magnesium salt
  • aluminum salt e.g. magnesium salt
  • zinc salt e.g. magnesium salt
  • the salt of polyhydroxyl monocarboxylic acid is selected from sodium gluconate (sodium salt of 2, 3, 4, 5, 6-pentahydroxyhexanoic acid) , zinc gluconate, sodium threonate (sodium salt of 2, 3, 4, 5-tetrahydroxypentanoic acid) , ammonium threonate, sodium erythronate (2, 3, 4-trihydroxybutanoic acid) , potassium erythronate, and mixture thereof.
  • the weight ratio of the silane coupling agent to the polyhydroxyl monocarboxylic acid is in the range of 0.5 to 5, preferably 1 to 3.
  • the weight ratio of the silane coupling agent to the rare earth element containing compound is in the range of 0.5 to 15, preferably 0.6 to 10.
  • the weight ratio of the silane coupling agent to the salt of polyhydroxyl monocarboxylic acid (if present) is in the range of 0.5 to 5, preferably 0.6 to 2.
  • the surface treatment compositions of the invention may also contain a solvent, such as water.
  • Water is used to dilute the surface treatment composition of the invention, and provides relatively long-term stability to the composition.
  • a composition that contains less than about 40%by weight water is more likely to polymerize or "gel" compared to a surface treatment composition with about 60%or greater by weight water under identical storage conditions.
  • the surface treatment compositions of the invention typically applied to the substrate will contain about 92%water or greater, such as 99%, it is to be understood that a surface treatment composition of the invention also includes a concentrated formulation composition with 60%to 92%by weight water. The end-user simply dilutes the concentrated formulation with additional water to obtain an optimal surface treatment composition concentration for a particular surface treatment application.
  • the surface treatment composition of the invention can be provided as a ready-to-use surface treatment composition, as a concentrated surface treatment composition that is diluted with water prior to use, as a replenishing composition, or as a multi-component coating system.
  • the concentration of each of the respective constituents of the surface treatment compositions will, of course, be dependent upon whether the surface treatment composition to be used is a replenishing surface treatment composition, a concentrated surface treatment composition, or a ready-to-use surface treatment composition.
  • a replenishing surface treatment composition can be provided to and used by an end-user to restore an optimal concentration of constituents of a surface treatment composition during the coating of substrates.
  • a replenishing surface treatment composition will necessarily have a higher concentration of cations of rare earth element or polyhydroxyl monocarboxylic acid than the surface treatment composition used to coat the substrate.
  • aqueous solution refers to a composition containing at least 50%by weight, or even 60%by weight of water based on the total weight of the composition.
  • the present invention also provides an aqueous surface treatment solution for light metallic material, comprising the surface treatment composition for light metallic material according to present invention and 60%to 99.9%, preferably 80%to 99.9%by weight of water based on the total weight of the composition.
  • the pH value of the aqueous solution is in the range of 1 to 6.5, preferably 2 to 6.3, and in other words, the aqueous surface treatment solution according to the present invention is an acidic solution.
  • other suitable solvents include those that have found particular utility in water borne coating technologies.
  • solvents examples include, but are not limited to, alcohols, such as methanol and ethanol, glycols, such as dipropylene glycol, and other glycol ethers, such as propylene glycol monobutyl ether and dipropylene glycol monobutyl ether.
  • the rare earth element containing compound is present in an amount of from 0.01%to 0.5%, and preferably from 0.03%to 0.3%, based on the weight of the surface treatment composition for light metallic material.
  • the silane coupling agent is present in an amount of from 0.01%to 0.5%, and preferably from 0.02%to 0.3%, based on the weight of the surface treatment composition for light metallic material.
  • the salt of polyhydroxyl monocarboxylic acid is present in an amount of from 0 to 0.5%, preferably 0.01%to 0.5%, and more preferably from 0.03%to 0.3%, based on the weight of the aqueous surface treatment solution.
  • the polyhydroxyl monocarboxylic acid is present in an amount of from 0.01%to 0.5%, and preferably from 0.03%to 0.4%, based on the weight of the aqueous surface treatment solution.
  • the present invention is directed to an aqueous surface treatment solution for light metallic material, comprising:
  • the percentage is based on the weight of the aqueous surface treatment solution for light metallic material.
  • the surface treatment compositions/solutions containing the polyhydroxyl monocarboxylic acids according to the present invention are storage stable and confer to a transparent coating film which exhibits an excellent oxidation/corrosion resistance on the light metallic material surface, and are superior in adhesion to painting materials.
  • the present invention does not rely on the formation of coatings that are essentially constituted of chromates, phosphates or hydroxides/oxides of the elements Zr, Ti and/or Hf. Consequently, within the aqueous solution of the present invention the amount of each of the elements Mn, Zn or Fe is preferably less than 500 ppm, preferably less than 100 ppm. It is as well preferred that the amount of each of the elements Zr, Ti or Hf in the aqueous solution is less than 50 ppm, more preferably less than 10 ppm, even more preferably less than 5 ppm.
  • the amount of phosphates in the aqueous solution is preferably less than 1000 ppm, more preferably less than 100 ppm calculated with respect to the element P.
  • the amount of each of the elements Ni, Co or Cu is less than 100 ppm, preferably less than 10 ppm in order to avoid electroless metallization of the substrate.
  • the surface treatment composition/solution for light metallic material can optionally comprise conventional additives known to a person skilled in the adhesive art.
  • Conventional additives which are compatible with the disclosed surface treatment composition/solution may simply be determined by combining a potential additive with the composition and determining if they remain homogenous.
  • suitable additives include, without limitation, solvents, corrosion inhibitors, defoamers, surfactants, UV-stabilizers, extenders, plasticizers, and pigments as are known in the art.
  • the total level of additives will vary depending on amount of each particular additive needed to provide the surface treatment composition/solution for light metallic material with desired properties.
  • the level of additives can be from 0 to about 10%, and preferably from about 0.1 to about 5%by weight of the total weight of the surface treatment solution.
  • the surface treatment compositions/solutions can be applied onto any suitable surface of metallic materials, such as light metals or their alloys, in any suitable manner.
  • the surface treatment compositions/solutions composition is spray applied over the substrate of magnesium, aluminum, or its alloy.
  • the surface treatment time may be from 30 sec to 10 min, and preferably from 1 min to 3 min.
  • the surface treatment composition/solution is prepared by combining the water with the polyhydroxyl monocarboxylic acid, the earth element containing compound, the silane coupling agent, and optionally with the salt of earth element containing compound.
  • the compositions are allowed to air dry at room temperature. Any suitable coating thickness can be employed, however it has been found that coating thickness of 10 to 1000 nm, preferably 20 to 100 nm have worked particularly well.
  • Various embodiments of the present invention also include a method for improving corrosion resistance of a metallic substrate, comprising:
  • the method may include additional steps that are conventional per se, such as rinsing, etching, de-smutting, conversion coating, and/or painting or some similar top coating process that puts into place an organic binder containing protective coating over the metal surface treated.
  • a panel of light metal such as aluminium or magnesium was treated with degreasing and/or cleaning chemicals by dipping or spraying. After degreasing/cleaning, water rinse is applied to clean the panel.
  • the cleaned light metal panel was treated with acidic or basic solution to get metal surface corroded so as to remove metal oxides, and water rinse is optional.
  • the light metal panel was treated with acidic or basic solution to remove the smut caused by etching, and ultrasonic rinse is optional.
  • a water rinse is optional.
  • conversion coating the light metal panel was treated with the surface treatment compositions according to the present invention for 30 seconds to 10 minutes, and a transparent film is formed on the metal surface. After the conversion coating, a water rinse is optional. Afterwards, the metal panel having the conversion coating film was treated for final top painting.
  • Coating films obtained by the surface treatment composition according to the present application are also within the scope of the invention.
  • Such coating films are (visually) transparent, possess excellent properties of corrosion resistance and confer to a coated metallic substrate having an appearance of metallic gloss and silvery color tone.
  • an article of manufacture comprising a basic coating film formed by the surface treatment composition or aqueous solution for light metallic material according to the present invention and coated on the article surface, and optionally at least one additional coating or paint film of painting material on the basic coating film.
  • the additional coating film next to the basic coating film have an excellent adhesion to the basic coating film.
  • the additional coating film has a thickness of 1 to 500 ⁇ m, preferably 10 to 100 ⁇ m.
  • Examples of painting materials may include an aqueous paint, anti-corrosive paint, oil-based paint, synthetic resin paint, enamel paint, lacquer, powder paint, vanish, primer, phenol resin paint, alkyd resin paint, amino alkyd resin paint, epoxy resin paint, vinyl resin paint, emulsion paint, polyester resin paint, polyurethane resin paint, water resin paint for metal, acryl resin paint, silicon paint, fluorine resin paint, spraying materials for construction, but not limited thereto.
  • Such an additional painting/coating layer may be formed by a variety of methods known in the art including the coating methods mentioned above. If necessary, additional drying, heat-treating, etc. may be performed.
  • the articles of manufacture can find particular utility in electronics such as lap tops, computer, display monitors, etc.
  • the aqueous solution of the surface treatment composition is storage stable and appears transparent after storing for 48 hours at room temperature.
  • the coating film obtained by the surface treatment composition, and coated substrate of light metallic material are corrosion resistant and rated as 8 or above after tested for 2 hours by Neutral Salt Spray Test according to ASTM B117.
  • the coating film exhibits excellent adhesion to painting materials and is classified as 5B level by cross-hatch adhesion test according to ASTM D3359.
  • Cerium (III) refers to Cerium (III) nitrate hexahydrate commercially available from Sinopharm Group.
  • Aminopropyltriethyoxysilane is commercially available from Jingzhou Jianghan Fine Chemical Co. Ltd., under the trade name of JH-A110.
  • Other materials in the examples are commercially available from Sinopharm Group, and used as they are.
  • a panel of AZ31B magnesium alloy was treated with Bonderite C-AK 305 (commercially available from Henkel, 5%) at 50°C for 3 min for degreasing/cleaning. A water rinse was then applied to clean the panel.
  • the cleaned light metal panel was treated with Bonderite I-IC 8242 (commercially available from Henkel, 10%) for 1 min to get metal surface corroded so as to remove metal oxides, and a water rinse was applied.
  • the panel was then treated with Bonderite I-IC 3506 (commercially available from Henkel, 2%) to remove the smut caused by etching, and an ultrasonic rinse and water rinse were applied.
  • the panel was treated with the surface treatment compositions according to the examples for 1 min to obtain a film of conversion coating formed on the panel surface with a thickness of about 40 nm.
  • Water rinse was applied to clean the conversion coating, and a PPG UVCL 1024V clear painting (containing mainly polyurethane modified acrylic resin) as final top painting was applied with a thickness of 10 to 15 ⁇ m.
  • the appearance of the conversion coatings was observed and shown in Tables 3 and 5, and other evaluations were made as follows and shown in Tables 3 to 5.
  • the working solutions as prepared were stored at room temperature. If the solution maintained transparent without formation of visible precipitates after 48 hours, it was marked with “Yes” , otherwise, it was marked with “No” .
  • the Neutral Salt Spray Test (NSST) according to ASTM B117 was used to evaluate the corrosion resistance of the coating films and coated metal surfaces. If the rating is 8 or above after tested for 2 hours, the corrosion resistance was considered as “Pass” , otherwise, it was marked with “Fail” .
  • the pH values of the working solutions were determined by a pH meter at 25 °C.
  • the painting compatibility of the conversion coatings with painting materials was evaluated by cross-hatch adhesion test according to ASTM D3359, in which the adhesion of coating films to a paint by applying and removing pressure-sensitive tape over lattice pattern cuts made in the paint
  • the inventive examples achieved excellent performance in all tests. For instance, as shown in Fig. 1, the appearance of the coated substrate of magnesium alloy treated by the inventive composition of Example 1 exhibited a metallic gloss and silvery color tone. As shown in Fig. 2, the test result of cross-hatch adhesion demonstrated an excellent adhesion of the inventive composition of Example 1 to paint coating. However, the comparative examples are not satisfactory in at least one test item.

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Abstract

Provided is a surface treatment composition for metallic material comprising a rare earth element containing compound, a silane coupling agent, and a polyhydroxyl monocarboxylic acid. Also provided is an aqueous surface treatment solution for light metallic material.

Description

Surface treatment composition for light metallic material Technical field
This invention relates to a surface treatment composition for light metallic material. In particular, the present invention relates to a surface treatment composition for light metal and its alloy and a transparent conversion coating thereof conferring to an excellent corrosion resistance and a reliable adhesion.
Background of the invention
Among the practically used metal materials, light metal materials such as aluminium and magnesium materials are the lightest ones and also have high specific strength and therefore, they have been applied in various fields such as interior and exterior parts for motor cars and two-wheeled vehicles, parts for household appliances, containers for storage such as bags and suitcases, goods for sports, parts for optical machinery and tools, sticks and further new fields in electronic industries such as computers and acoustics. However, the light metal materials, especially the magnesium materials are the most active metal materials and accordingly, it has been difficult to use them per se without any treatment because of their low corrosion resistance.
As for surface treating methods for improving the corrosion resistance of the light metal materials, there have conventionally been used, for instance, chemical conversion treatments, anodization treatments and coating and plating techniques. For example, applying conversion coatings, in general, is a well-known method of providing light metals and their alloys with one or more layers or coatings that impart increased corrosion resistance and adhesion of subsequently applied finishes/coatings (i.e., lacquer, enamel, vanish, shellac, topcoat, and the like) to the metals.
In addition, when imparting decorative properties to articles of light metal materials, such as magnesium materials while making the most use of the gloss and color tone of the metal substrate surface thereof, the surface of the articles cannot be subjected to painting. However, the surface of the magnesium material is highly susceptible to oxidation and therefore, the article should be subjected to any surface treatment to maintain the initial gloss and color tone of the metal substrate surface thereof.
The coating obtained through the conventional chemical conversion treatment or anodization treatment using chromic acid or a bichromate gets colored. In addition, such treatments will produce hexavalent chromium ion in waste liquid, which does not meet the requirement of environment protection. Therefore, it is necessary to find a surface treatment solution free of hexavalent chromium ion for light metal materials to achieve corrosion resistance, adhesiveness and gloss and color tone as desired.
For instance, US 7695771 B2 discloses a process for forming a non-chromate conversion coating on surfaces of magnesium or magnesium alloys by using a process solution which is an acidic aqueous solution comprising at least one fluorosilicon acid, optionally, at least one water-soluble pH adjustment agent, optionally, at least one surfactant and optionally, aluminum as cations or as at least one compound or any combination of these. However, the conversion coating disclosed in the patent is colorful and well-visible.
US 7819989 B2 discloses a composition for surface treatment of aluminum, an aluminum alloy, magnesium or a magnesium alloy comprising: (1) compound A containing at least one metal element selected from the group consisting of Hf (IV) , Ti (IV) and Zr (IV) , (2) fluorine-containing compound of a sufficient amount to make fluorine exist in the composition in an amount of at least 5 times the molarity of the total molarity of the metal contained in the above-mentioned compound A, (3) at least one metal ion B selected from the group of alkaline earth metals, (4) at least one metal ion C selected from the group consisting of Al, Zn, Mg, Mn and Cu, and (5) nitric ion. However, the surface treatment composition will produce fluoride ion in waste liquid, which is not friendly to environment.
US 6773516 B2 discloses an aqueous acidic solution for forming a rare earth element containing conversion coating on the surface of a metal, said solution being substantially chromate-free and including effective quantities of at least one cerium (III) containing species, an oxidant and at least one accelerator comprising a metal selected from Sb, Bi, Te, and Se. However, the conversion coating thus produced is in yellow color.
US 6200693 B2 discloses an aqueous liquid composition for treating the surfaces of light metals and light metal alloys, said liquid composition having a pH value within a range from 1.0 to 7.0 and consisting essentially of water and the following components: (A) from 0.01 to 50 g/L of a component selected from the group consisting of permanganic acid, water soluble salts thereof, and mixtures of any two or more of permanganic acid and any of its water soluble salts; and (B) from 0.01 to 20 g/L of a component selected from the group consisting of water soluble compounds of titanium, water soluble compounds of zirconium, and mixtures of any two or more of said water soluble compounds of titanium and zirconium. However, the conversion coating thus produced may be colorful due to the use of permanganic acid in the composition.
US 9290846 B2 relates to a composition for surface treatment of aluminum alloys, comprising a conducting polymer dispersion (such as polypyrrole) , at least one silane and inorganic metallic salts, wherein a pH of the composition is between 1.0 and 6.0, and wherein the inorganic metallic salts comprise at least one zirconium salt and at least one cerium nitrate salt, but the color of the resulting conversion coating depends upon the metallic surface and the bath/spray parameters.
US 8609755 B2 relates to a storage stable composition for treating metal surfaces such as aluminum, consisting essentially of: a) an aqueous solution of partial and/or complete condensate of ureidosilane,  b) a stabilizing agent selected from the group consisting of alcohols, glycols, triol, polyols, glycol ethers, esters, ketones, pyrolidones and polyether silanes; and c) a colloidal cerium oxide.
CN 102115880 A teaches a surface treatment composition for light metal or its alloy comprising a titanium containing compound, a vanadium containing compound and an organic acid, wherein the organic acid contains 1 to 100 carbon atoms and 2 to 50 oxygen atoms.
WO 2016044972 A1 discloses an alkaline aqueous composition for the pretreatment of metal substrates such as aluminum alloy, comprising a source of cerium cations and an amino-functional organosilane.
Unfortunately, while the use of chrome solution has decreased, and while various surface treatment compositions have been suggested and used in place of chromate-based coatings, chromate-free pretreatment coatings for substrates of metal, particularly light metals and their alloys, which exhibit the corrosion protection, adhesion and metallic gloss/color tone have not been adequately provided in the art.
Accordingly, it is an object of the present invention to provide a surface treatment composition for light metallic material, especially aluminium, magnesium or its alloy, which can eliminate the problems associated with the conventional surface treatment composition.
Summary of the invention
The present invention provided the surface treatment composition and its solution for light metal or its alloy as well as the surface treatment method which overcome the abovementioned disadvantage of present hexavalent chromium ion free surface treatment method of light metal materials. The surface treatment composition in this invention is free of hexavalent chromium ion and could significantly improve the corrosion resistance of light metal and its alloy. The surface treatment solution in this invention is stable and transparent. Besides, the surface treatment method in this invention is simple and suitable for industrial production.
The present invention, in general, provides a surface treatment composition for light metallic material, especially light metallic material, comprising:
(1) a rare earth element containing compound,
(2) a silane coupling agent, and
(3) a polyhydroxyl monocarboxylic acid.
The present invention also provides an aqueous surface treatment solution for light metallic material, comprising the surface treatment composition for light metallic material according to the present invention and water, a conversion coating prepared by the surface treatment composition or the  aqueous surface treatment solution for light metallic material, and an article of manufacture, comprising a conversion coating prepared by the surface treatment composition for light metallic material.
Furthermore, the present invention provides a method for improving corrosion resistance of a metallic substrate, comprising:
(1) providing the surface treatment composition for light metallic material or its aqueous surface treatment solution according to the present invention,
(2) contacting the metallic substrate with the surface treatment composition or the aqueous surface treatment solution for light metallic material, and
(3) allowing the surface treatment composition for light metallic material to dry to form a coating on the substrate.
Brief description of the figures
Figure 1 illustrates the appearance of a coated magnesium alloy substrate treated by the working solution of Example 1.
Figure 2 illustrates the test result of a coated magnesium alloy substrate treated by the working solution of Example 1 and having a top coat according to ASTM D3359.
Detailed description of the invention
In the following passages the present invention is described in more detail. Each aspect so described may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.
In the context of the present invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.
As used herein, the singular forms “a” , “an” and “the” include both singular and plural referents unless the context clearly dictates otherwise.
The terms “comprising” , “comprises” and “comprised of” as used herein are synonymous with “including” , “includes” or “containing” , “contains” , and are inclusive or open-ended and do not exclude additional, non-recited members, elements or process steps.
The recitation of numerical end points includes all numbers and fractions subsumed within the respective ranges, as well as the recited end points.
All references cited in the present specification are hereby incorporated by reference in their entirety.
Unless otherwise defined, all terms used in the disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of the ordinary skill in the art to which this invention belongs to. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.
According to the present invention, the surface treatment composition for light metallic material comprises a rare earth element containing compound. The rare earth element containing compound is a compound containing yttrium, lanthanum and/or cerium, and preferably is a cerium containing compound in view of cost-efficiency. In one embodiment, the rare earth element containing compound is a water-soluble compound so as to be further formulated as aqueous solution. By term "water-soluble" used herein it means that more than 5g/L of rare earth element containing compound can be dissolved into deionized water at 20 ℃ while still a homogenous solution is attained without visible precipitates over a period of 24 h.
The cerium containing compounds in the present invention may be selected from tetravalent cerium compounds, trivalent cerium compounds, and/or hydrate of the same. Lanthanide ions as cerium (III) and cerium (IV) forming insoluble hydroxides show low toxicity and are economically competitive products, since cerium is relatively abundant in nature. Therefore, tetravalent and trivalent cerium compounds have been investigated to develop corrosion protection systems for light metallic materials as alternative to chromates.
Specific examples of tetravalent and trivalent cerium compounds include cerium (IV) hexanitrates such as cerium (IV) diammonium nitrate and potassium cerium (IV) nitrate; cerium (IV) tetraammonium sulfate; and cerium (IV) sulfate. The cerium compounds may be hydrates such as cerium (IV) tetraammonium sulfate dihydrate, and cerium (IV) sulfate tetrahydrate. Two or more of the tetravalent cerium compounds may be used in combination.
The trivalent cerium containing compound used in the present invention may be any one of cerium (III) acetate, cerium (III) ammonium nitrate, cerium (III) carbonate, cerium (III) chloride, cerium (III) fluoride, cerium (III) nitrate, cerium (III) sulfate, cerium (III) bromide, cerium (III) iodide, cerium (III) oxalate, cerium (III) perchloride, cerium (III) sulfide, and hydrates of the same. Two or more of the foregoing trivalent cerium compounds may be used in combination.
The tetravalent cerium compound (s) and the trivalent cerium compound (s) may be used singly or in combination. Preferably, the cerium containing compounds are trivalent cerium containing compound, and more preferably is selected from cerium (III) acetate, cerium (III) ammonium nitrate, cerium (III) carbonate, cerium (III) nitrate, hydrates of the same and mixture thereof.
The surface treatment composition for light metallic material in the present invention also comprises a silane coupling agent. It is known in the art that silane coupling agents can be added in the surface treatment compositions for light metallic materials to improve the adhesiveness of the coating formed on the metal surface.
There is no limitation to the silane coupling agents to be used in the surface treatment compositions, as long as the silane coupling agents are compatible to the rare earth element containing compound, such as the water-soluble cerium salts and other components contained in the surface treatment composition.
The silane coupling agents may have an amino functional group or epoxy functional group. The amino or epoxy functional silane may comprise C 2-C 10-alkoxy-groups.
The silane coupling agent may have the general structure R 1-Si-X 3, where R 1 is a reactive organofunctional group and at least one of X is a hydrolysable group and others are optionally substituted alkyl or an aryl group containing 1 to 10 carbon atoms. The hydrolysable group may be selected from alkoxy, acyloxy, halogen or amine. For example, the alkoxy may be a C 1-C 6 alkoxy (e.g. a methoxy or ethoxy group) ; the acyloxy may be a phenyloxy, and; the halogen may be may be a chloride or a bromide.
R 1 may be an optionally substituted alkyl or an aryl group containing 1-10 carbon atoms, e.g. 2-10 carbon atoms. If R 3 is a substituted alkyl or an aryl group containing 1-10 carbon atoms, R 1 is preferably substituted with one or more amine or epoxy functional groups. In these cases, the silane coupling agent may then be described as an amino functional silane or an epoxy functional silane respectfully.
Some exemplary epoxy functional silanes include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane or beta- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane.
Suitably, R 3 is an alkyl or an aryl group containing 1 to 10 carbon atoms substituted with one or more amine groups, or an aryl group (e.g. phenyl group) containing 5 to 10 carbon atoms substituted with one or more amine groups. The amine groups may be one or more primary, secondary or tertiary amine groups.
A suitable amine functional silane coupling agent for use in the surface treatment composition of the present invention has the structure: (R 2-O)  3-Si-R 3-NH 2, wherein R 2 is an alkyl group containing 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms and most preferably is a methyl group, R 3 is an alkylene moiety containing 1 to 10 carbon atoms optionally substituted with an amine group. Examples of amine functional silane coupling agent are aminomethylaminopropyltrimethoxylsilane ( (MeO)  3-Si- (CH 2)  3-NH- (CH 2) -NH 2) , aminopropyltrimethoxysilane ( (MeO)  3-Si- (CH 2)  3-NH 2) , and/or aminopropyltriethoxysilane ( (EtO)  3-Si- (CH 2)  3-NH 2) .
Other examples of silane coupling agents suitable for the present invention include but not limited to 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, 3- [2- (2-aminoethylamino) ethylamino] propyltrimethoxysilane, N- (2-aminoethyl) -3-aminoisobutylmethyldimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltris (2-ethylhexoxy) silane, N- (6-aminohexyl) aminopropyltrimethoxysilane, m-aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane, o-aminophenyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, aminopropyltrimethoxysilane, aminopropylmethyldimethoxysilane, aminopropyltriethoxysilane, aminopropylmethyldiethoxysilane, aminophenyltrimethoxysilane, 4-amino-3-dimethylbutyltrimethoxysilane, 4-amino-3-dimethylbutylmethyldimethoxysilane, 4-amino-3-dimethylbutyltriethoxysilane, 4-amino-3-dimethylbutylmethyldiethoxysilane, N-phenyl-aminopropyltrimethoxysilane, N-naphthyl-aminopropyltrimethoxysilane, N-phenyl-aminopropylmethyldimethoxysilane, N-naphthyl-aminopropylmethyldimethoxysilane, N- (n-butyl) aminopropyltrimethoxysilane, N- (n-butyl) aminopropylmethyldimethoxysilane, N-ethyl-aminopropyltrimethoxysilane, N-ethyl-aminopropylmethyldimethoxysilane, N-methyl-aminopropyltrimethoxysilane, N-methyl-gamma aminopropylmethyldimethoxysilane, N-beta- (aminoethyl) -aminopropyltrimethoxysilane, N-beta- (aminoethyl) -aminopropyltriethoxysilane, N-beta (aminoethyl) aminopropylmethyldimethoxysilane, N-beta- (aminoethyl) aminopropylmethyldiethoxysilane, N-3- [amino (dipropyleneoxy) ] aminopropyltrimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, N- (6-aminohexyl) aminopropyltrimethoxysilane, N- (2-aminoethyl) -11-aminoundecyltrimethoxysilane, bis (trimethoxysilylpropyl) amine, (3-trimethoxysilylpropyl) diethylenetriamine, (aminoethylamino) -3-isobutyldimethylmethoxysilane, (cyclohexylaminomethyl) triethoxysilane, (N, N-diethyl-3-aminopropyl) trimethoxysilane, (phenylaminomethyl) methyldimethoxysilane, 11-aminoundecyltriethoxysilane, 2- (2-pyridylethyl) thiopropyltrimethoxysilane, 2- (4-pyridylethyl) triethoxysilane, 2- (trimethoxysilylethyl) pyridine, 3- (1, 3-dimethylbutylidene) aminopropyltriethoxysilane, 3- (2-imidazolin-1-yl) propyltriethoxysilane, 3- (m-aminophenoxy) propyltrimethoxyaminopropylsilanetriol, 3- (m-aminophenoxy) propyltrimethoxysilane, 3- (N, N-dimethylaminopropyl) trimethoxysilane, 3- (N-allylamino) propyltrimethoxysilane, 3-aminopropyldiisopropylethoxysilane, 3-aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltris (methoxyethoxyethoxy) silane, 4-aminobutyltriethoxysilane, acetamidopropyltrimethoxysilane, aminopropylsilanetriol, bis (2-hydroxyethyl) -3-aminopropyltriethoxysilane, bis (methyldiethoxysilylpropyl) amine, bis (methyldimethoxysilylpropyl) n-methylamine, bis (triethoxysilylpropyl) amine, bis (trimethoxysilylpropyl) urea, bis [ (3-trimethoxysilyl) propyl] ethylenediamine, bis [3- (triethoxysilyl) propyl] urea,  diethylaminomethyltriethoxysilane, N- (2-aminoethyl) -3-aminoisobutylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropylsilanetriol, n- (2-aminoethyl) -3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (3-aminopropyldimethylsila) aza-2, 2-dimethyl-2-silacyclopentane, N- (3-triethoxysilylpropyl) 4, 5-dihydroimidazole, N- (3-trimethoxysilylpropyl) pyrrole, N- (6-aminohexyl) aminomethyltriethoxysilane, N- (6-aminohexyl) aminomethyltrimethoxysilane, N, N, N-trimethyl-3- (trimethoxysilyl) -1-propanaminium, N, N-dioctyl-N’-triethoxysilylpropylurea, N- [5- (trimethoxysilyl) -2-aza-1-oxopentyl] caprolactam, N-3- [ (amino (polypropylenoxy) ] aminopropyltrimethoxysilane, N-butylaminopropyltrimethoxysilane, N-cyclohexylaminopropyltrimethoxysilane, N-ethylaminoisobutylmethyldiethoxysilane, N-ethylaminoisobutyltrimethoxysilane, N-phenylaminomethyltriethoxysilane, n-trimethoxysilylpropylcarbamoylcaprolactam, ureidopropyltriethoxysilane, ureidopropyltrimethoxysilane, and mixture thereof, and preferably is selected from N-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, bis [3- (trimethoxysilyl) propyl] amine.
The amine functional silane coupling agent and/or epoxy functional silane coupling agent can be singly used or in combination.
The surface treatment compositions for light metallic material according to the present invention also comprises a polyhydroxyl monocarboxylic acid. The term “polyhydroxyl monocarboxylic acid” used herein should be understood in a broad sense, and it refers to a source of an organic acid having one carboxylic group and two or more hydroxyl groups, preferably from 2 to 6 hydroxyl groups including free acid form and lactone form, but not including salt form. The salt of polyhydroxyl monocarboxylic acid may be further added in the surface treatment composition, in combination with the free acid form and/or lactone form of polyhydroxyl monocarboxylic acid. The lactone of a polyhydroxyl monocarboxylic acid transforms to free acid when it dissolves in solvent such as water. The polyhydroxyl monocarboxylic acid may exist as stereoisomers as D, L, and DL forms.
In one embodiment, the polyhydroxyl monocarboxylic acid has the structure represented by
R 4R 5R 6-COOH
wherein, R 4 is alkyl, alkoxyl, aralkyl, or aryl group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH, R 5 and R 6 are each independently alkylene, alkoxylene, aralkylene or arylene group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH, with the proviso that the number of hydroxyl groups in R 4, R 5 and R 6 is two or more, and preferably from 2 to 6.
In one particular embodiment, R 6 is hydroxymethylene, and the polyhydroxyl monocarboxylic acid is an α-hydroxyl acid having one carboxyl group and two or more hydroxyl groups. In another particular embodiment, R 4 is linear alkyl or alkoxyl optionally substituted by OH, and preferably is linear alkyl optionally substituted by OH, and R 5 and R 6 are each independently linear alkylene or alkoxylene  optionally substituted by OH, and preferably is linear alkylene optionally substituted by OH. In yet another particular embodiment, R 4, R 5 and R 6 are all saturated groups. In yet another particular embodiment, R 4, R 5 and R 6 have 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms in total.
Suitably, the examples of such polyhydroxyl monocarboxylic acid include but not limited to 2, 3-dihydroxypropanoic acid, 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, 2, 3, 4, 5, 6, 7-hexahydroxyheptanoic acid, 2, 3, 4, 5, 6, 7, 8-hexahydroxyoctanoic acid, 2, 3-dihydrobutanoic acid, 2, 4-dihydrobutanoic acid, 2, 3-dihydropentanoic acid, 2, 4-dihydropentanoic acid, 2, 5-dihydropentanoic acid, 2, 3, 4-trihydropentanoic acid, 2, 3, 5-trihydropentanoic acid, 2, 4, 5-trihydropentanoic acid, 2, 3-dihydroxyhexanoic acid, 2, 4-dihydroxyhexanoic acid, 2, 5-dihydroxyhexanoic acid, 2, 6-dihydroxyhexanoic acid, 2, 3, 4-trihydrohexanoic acid, 2, 3, 5-trihydrohexanoic acid, 2, 3, 6-trihydrohexanoic acid, 2, 4, 5-trihydrohexanoic acid, 2, 4, 6-trihydrohexanoic acid, 2, 5, 6-trihydrohexanoic acid, 2, 3, 4, 5-tetrahydrohexanoic acid, 2, 3, 4, 6-tetrahydrohexanoic acid, 2, 4, 5, 6-tetrahydrohexanoic acid, 2, 3, 5, 6-tetrahydrohexanoic acid, lactone, isomer, derivative, and mixture thereof.
Preferably, the polyhydroxyl monocarboxylic acid has a linear and saturated carbon chain containing 4 to 8 carbon atoms, such as 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, 2, 3, 4, 5, 6, 7-hexahydroxyheptanoic acid, 2, 3, 4, 5, 6, 7, 8-hexahydroxyoctanoic acid, and lactone, isomer, derivative, and mixture thereof., and more preferably is 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, and lactone, isomer, derivative, and mixture thereof.
Other examples of polyhydroxyl monocarboxylic acids suitable for the present invention includes 2, 3-dihydroxy-2-methylbutyric acid, 2-methylglyceric acid, glyceric acid, 2- (hydroxymethyl) -3-hydroxypropionic acid, 2, 2- (dihydroxymethyl) propionic acid, 2, 3-dihydroxyisovaleric acid, 2, 3-dihydroxy-3-methylbutyric acid, 2-hydroxymethyl-4-hydroxybutanoic acid, 2, 4-dihydroxy-3, 3-dimethylbutanoic acid, 2, 3-dihydroxy-3-methylpentanoic acid, 2, 4-dihydroxy-3-methylpentanoic acid, 2, 5-dihydroxy-3-methylpentanoic acid, 3, 5-dihydroxy-3-methylpentanoic acid, 2, 2-bis (hydroxymethyl) butanoic acid, 3, 5-dihydroxy-2, 3-dimethylpentanoic acid, 3, 5-dihydroxy-3, 4-dimethylpentanoic acid, 2, 4-dihydroxy-2, 4-dimethylpentanoic acid, 2- (1-hydroxyethyl) -4-hydroxypentanoic acid, 2, 3-dihydroxy-2-isopropylbutanoic acid, 1- (hydroxymethyl) -2-hydroxyethyl hydroxyacetate, 2-methylthreonic acid, 3-methyl-2, 3, 4-trihydroxybutyric acid, 3-hydroxy-2, 2-bis (hydroxymethyl) propionic acid, xyloisosaccharic acid, 2-methylerythronic acid, digitoxonic acid, isomer, derivative, and mixture thereof.
The polyhydroxyl monocarboxylic acids can be singly used or in combination. In one particular embodiment, the polyhydroxyl monocarboxylic acid is selected from 2, 3, 4, 5, 6-pentahydroxyhexanoic acid (such as D-gluconic acid) , lactone of 2, 3, 4, 5, 6-pentahydroxyhexanoic acid (such as D- gluconolactone) , 2, 3, 4-trihydroxybutanoic acid (such as D-erythronic acid) , lactone of 2, 3, 4-trihydroxybutanoic acid (such as D-erythronolactone) , and mixture thereof.
According to the present invention, the polyhydroxyl monocarboxylic acid may be used with it salts in combination, and in one embodiment, the surface treatment composition according to the present invention further comprises a salt, preferably a water-soluble salt, of polyhydroxyl monocarboxylic acid, such as alkali metal salt (e.g. salt of sodium, potassium or lithium) , alkali earth metal salt (e.g. magnesium salt) , aluminum salt, zinc salt, and ammonium salt of polyhydroxyl monocarboxylic acid.
Preferably, the salt of polyhydroxyl monocarboxylic acid is selected from sodium gluconate (sodium salt of 2, 3, 4, 5, 6-pentahydroxyhexanoic acid) , zinc gluconate, sodium threonate (sodium salt of 2, 3, 4, 5-tetrahydroxypentanoic acid) , ammonium threonate, sodium erythronate (2, 3, 4-trihydroxybutanoic acid) , potassium erythronate, and mixture thereof.
In the surface treatment composition for light metallic material according to the present invention, the weight ratio of the silane coupling agent to the polyhydroxyl monocarboxylic acid is in the range of 0.5 to 5, preferably 1 to 3. The weight ratio of the silane coupling agent to the rare earth element containing compound is in the range of 0.5 to 15, preferably 0.6 to 10. The weight ratio of the silane coupling agent to the salt of polyhydroxyl monocarboxylic acid (if present) is in the range of 0.5 to 5, preferably 0.6 to 2.
The surface treatment compositions of the invention may also contain a solvent, such as water. Water is used to dilute the surface treatment composition of the invention, and provides relatively long-term stability to the composition. For example, a composition that contains less than about 40%by weight water is more likely to polymerize or "gel" compared to a surface treatment composition with about 60%or greater by weight water under identical storage conditions. Although the surface treatment compositions of the invention typically applied to the substrate will contain about 92%water or greater, such as 99%, it is to be understood that a surface treatment composition of the invention also includes a concentrated formulation composition with 60%to 92%by weight water. The end-user simply dilutes the concentrated formulation with additional water to obtain an optimal surface treatment composition concentration for a particular surface treatment application.
The surface treatment composition of the invention can be provided as a ready-to-use surface treatment composition, as a concentrated surface treatment composition that is diluted with water prior to use, as a replenishing composition, or as a multi-component coating system.
The concentration of each of the respective constituents of the surface treatment compositions will, of course, be dependent upon whether the surface treatment composition to be used is a replenishing surface treatment composition, a concentrated surface treatment composition, or a ready-to-use surface treatment composition. A replenishing surface treatment composition can be provided to and  used by an end-user to restore an optimal concentration of constituents of a surface treatment composition during the coating of substrates. As a result, a replenishing surface treatment composition will necessarily have a higher concentration of cations of rare earth element or polyhydroxyl monocarboxylic acid than the surface treatment composition used to coat the substrate.
As used therein, “aqueous solution” refers to a composition containing at least 50%by weight, or even 60%by weight of water based on the total weight of the composition. The present invention also provides an aqueous surface treatment solution for light metallic material, comprising the surface treatment composition for light metallic material according to present invention and 60%to 99.9%, preferably 80%to 99.9%by weight of water based on the total weight of the composition. The pH value of the aqueous solution is in the range of 1 to 6.5, preferably 2 to 6.3, and in other words, the aqueous surface treatment solution according to the present invention is an acidic solution. In addition to water, other suitable solvents include those that have found particular utility in water borne coating technologies. Examples of other suitable solvents include, but are not limited to, alcohols, such as methanol and ethanol, glycols, such as dipropylene glycol, and other glycol ethers, such as propylene glycol monobutyl ether and dipropylene glycol monobutyl ether.
In the aqueous surface treatment solution, the rare earth element containing compound is present in an amount of from 0.01%to 0.5%, and preferably from 0.03%to 0.3%, based on the weight of the surface treatment composition for light metallic material.
In the aqueous surface treatment solution, the silane coupling agent is present in an amount of from 0.01%to 0.5%, and preferably from 0.02%to 0.3%, based on the weight of the surface treatment composition for light metallic material.
In the aqueous surface treatment solution, the salt of polyhydroxyl monocarboxylic acid is present in an amount of from 0 to 0.5%, preferably 0.01%to 0.5%, and more preferably from 0.03%to 0.3%, based on the weight of the aqueous surface treatment solution.
In the aqueous surface treatment solution, the polyhydroxyl monocarboxylic acid is present in an amount of from 0.01%to 0.5%, and preferably from 0.03%to 0.4%, based on the weight of the aqueous surface treatment solution.
In one particular embodiment, the present invention is directed to an aqueous surface treatment solution for light metallic material, comprising:
(1) 0.01%to 0.5%, and preferably from 0.03%to 0.3%of a rare earth element containing compound,
(2) 0.01%to 0.5%, and preferably from 0.02%to 0.3%of a silane coupling agent, and
(3) 0.01%to 0.5%, and preferably from 0.03%to 0.4%of a polyhydroxyl monocarboxylic acid,
(4) 0 to 0.5%, and preferably from 0.03%to 0.3%of a salt of polyhydroxyl monocarboxylic acid, and
(5) 60%to 99.9%, and preferably from 80%to 99.9%of water,
in which the percentage is based on the weight of the aqueous surface treatment solution for light metallic material.
It is known in the art that organic acids have coordination effect with metal cations to form coordinated complex in surface treatment solutions so as to avoid the precipitation of metal cations and increase the stability of surface treatment solutions. Surprisingly, the inventors have found that the surface treatment compositions/solutions containing the polyhydroxyl monocarboxylic acids according to the present invention are storage stable and confer to a transparent coating film which exhibits an excellent oxidation/corrosion resistance on the light metallic material surface, and are superior in adhesion to painting materials.
The present invention does not rely on the formation of coatings that are essentially constituted of chromates, phosphates or hydroxides/oxides of the elements Zr, Ti and/or Hf. Consequently, within the aqueous solution of the present invention the amount of each of the elements Mn, Zn or Fe is preferably less than 500 ppm, preferably less than 100 ppm. It is as well preferred that the amount of each of the elements Zr, Ti or Hf in the aqueous solution is less than 50 ppm, more preferably less than 10 ppm, even more preferably less than 5 ppm. Moreover, the amount of phosphates in the aqueous solution is preferably less than 1000 ppm, more preferably less than 100 ppm calculated with respect to the element P. In yet another preferred embodiment the amount of each of the elements Ni, Co or Cu is less than 100 ppm, preferably less than 10 ppm in order to avoid electroless metallization of the substrate.
The surface treatment composition/solution for light metallic material can optionally comprise conventional additives known to a person skilled in the adhesive art. Conventional additives which are compatible with the disclosed surface treatment composition/solution may simply be determined by combining a potential additive with the composition and determining if they remain homogenous. Non-limiting examples of suitable additives include, without limitation, solvents, corrosion inhibitors, defoamers, surfactants, UV-stabilizers, extenders, plasticizers, and pigments as are known in the art.
The total level of additives will vary depending on amount of each particular additive needed to provide the surface treatment composition/solution for light metallic material with desired properties. The level of additives can be from 0 to about 10%, and preferably from about 0.1 to about 5%by weight of the total weight of the surface treatment solution.
The surface treatment compositions/solutions can be applied onto any suitable surface of metallic materials, such as light metals or their alloys, in any suitable manner. In at least one embodiment, the surface treatment compositions/solutions composition is spray applied over the substrate of magnesium, aluminum, or its alloy. The surface treatment time may be from 30 sec to 10 min, and preferably from 1 min to 3 min. Generally, the surface treatment composition/solution is prepared by combining the water with the polyhydroxyl monocarboxylic acid, the earth element containing  compound, the silane coupling agent, and optionally with the salt of earth element containing compound. The compositions are allowed to air dry at room temperature. Any suitable coating thickness can be employed, however it has been found that coating thickness of 10 to 1000 nm, preferably 20 to 100 nm have worked particularly well.
Various embodiments of the present invention also include a method for improving corrosion resistance of a metallic substrate, comprising:
(1) providing the surface treatment composition or solution for light metallic material according to the present invention,
(2) contacting the surface of metallic substrate with the surface treatment composition or solution, and
(3) allowing the surface treatment composition for light metallic material to dry to form a coating on the substrate.
The method may include additional steps that are conventional per se, such as rinsing, etching, de-smutting, conversion coating, and/or painting or some similar top coating process that puts into place an organic binder containing protective coating over the metal surface treated.
For example, a panel of light metal such as aluminium or magnesium was treated with degreasing and/or cleaning chemicals by dipping or spraying. After degreasing/cleaning, water rinse is applied to clean the panel. The cleaned light metal panel was treated with acidic or basic solution to get metal surface corroded so as to remove metal oxides, and water rinse is optional. Then the light metal panel was treated with acidic or basic solution to remove the smut caused by etching, and ultrasonic rinse is optional. After the de-smutting, a water rinse is optional. In conversion coating, the light metal panel was treated with the surface treatment compositions according to the present invention for 30 seconds to 10 minutes, and a transparent film is formed on the metal surface. After the conversion coating, a water rinse is optional. Afterwards, the metal panel having the conversion coating film was treated for final top painting.
Coating films obtained by the surface treatment composition according to the present application are also within the scope of the invention. Such coating films are (visually) transparent, possess excellent properties of corrosion resistance and confer to a coated metallic substrate having an appearance of metallic gloss and silvery color tone. It is also disclosed herein an article of manufacture comprising a basic coating film formed by the surface treatment composition or aqueous solution for light metallic material according to the present invention and coated on the article surface, and optionally at least one additional coating or paint film of painting material on the basic coating film. In particular, the additional coating film next to the basic coating film have an excellent adhesion to the basic coating film. Suitably, the additional coating film has a thickness of 1 to 500 μm, preferably 10 to 100 μm. Examples of painting materials may include an aqueous paint, anti-corrosive paint, oil-based paint, synthetic resin paint, enamel paint, lacquer, powder paint, vanish, primer, phenol resin paint, alkyd  resin paint, amino alkyd resin paint, epoxy resin paint, vinyl resin paint, emulsion paint, polyester resin paint, polyurethane resin paint, water resin paint for metal, acryl resin paint, silicon paint, fluorine resin paint, spraying materials for construction, but not limited thereto. Such an additional painting/coating layer may be formed by a variety of methods known in the art including the coating methods mentioned above. If necessary, additional drying, heat-treating, etc. may be performed. The articles of manufacture can find particular utility in electronics such as lap tops, computer, display monitors, etc.
According to the present invention, the aqueous solution of the surface treatment composition is storage stable and appears transparent after storing for 48 hours at room temperature.
According to the present invention, the coating film obtained by the surface treatment composition, and coated substrate of light metallic material are corrosion resistant and rated as 8 or above after tested for 2 hours by Neutral Salt Spray Test according to ASTM B117.
According to the present invention, the coating film exhibits excellent adhesion to painting materials and is classified as 5B level by cross-hatch adhesion test according to ASTM D3359.
The following examples are intended to assist one skilled in the art to better understand and practice the present invention. The scope of the invention is not limited by the examples but is defined in the appended claims. All parts and percentages are based on weight unless otherwise stated.
Examples
Working solutions
The following materials were used in the examples. Cerium (III) refers to Cerium (III) nitrate hexahydrate commercially available from Sinopharm Group. Aminopropyltriethyoxysilane is commercially available from Jingzhou Jianghan Fine Chemical Co. Ltd., under the trade name of JH-A110. Other materials in the examples are commercially available from Sinopharm Group, and used as they are.
A multitude of working solutions were prepared according to the formulations listed in Tables 1 and 2. Organic acid (if present) , lactone/salt of polyhydroxyl monocarboxylic acid (if present) and cerium (III) nitrate hexahydrate, and silane coupling agent were added to deionized water and mixed for 10 min. The percentage of rare earth element containing compound (such as cerium (III) nitrate) was calculated as the weight percentage of rare earth element in the working solution, while the percentages of organic acids, salts, lactones, and silanes were calculated as the weight percentage of the compounds in the surface treatment solution.
Table 1. Formulations of inventive working solutions (in weight percentage)
Figure PCTCN2018076596-appb-000001
Table 2. Formulations of comparative working solutions (in weight percentage)
Figure PCTCN2018076596-appb-000002
Conversion Coating
A panel of AZ31B magnesium alloy was treated with Bonderite C-AK 305 (commercially available from Henkel, 5%) at 50℃ for 3 min for degreasing/cleaning. A water rinse was then applied to clean the panel. The cleaned light metal panel was treated with Bonderite I-IC 8242 (commercially available from Henkel, 10%) for 1 min to get metal surface corroded so as to remove metal oxides, and a water rinse was applied. The panel was then treated with Bonderite I-IC 3506 (commercially available from Henkel, 2%) to remove the smut caused by etching, and an ultrasonic rinse and water rinse were applied. The panel was treated with the surface treatment compositions according to the examples for 1 min to obtain a film of conversion coating formed on the panel surface with a thickness of about 40 nm. Water rinse was applied to clean the conversion coating, and a PPG UVCL 1024V clear painting  (containing mainly polyurethane modified acrylic resin) as final top painting was applied with a thickness of 10 to 15 μm. The appearance of the conversion coatings was observed and shown in Tables 3 and 5, and other evaluations were made as follows and shown in Tables 3 to 5.
Solution Stability
The working solutions as prepared were stored at room temperature. If the solution maintained transparent without formation of visible precipitates after 48 hours, it was marked with “Yes” , otherwise, it was marked with “No” .
NSST
The Neutral Salt Spray Test (NSST) according to ASTM B117 was used to evaluate the corrosion resistance of the coating films and coated metal surfaces. If the rating is 8 or above after tested for 2 hours, the corrosion resistance was considered as “Pass” , otherwise, it was marked with “Fail” .
pH Value
The pH values of the working solutions were determined by a pH meter at 25 ℃.
Painting compatibility
The painting compatibility of the conversion coatings with painting materials was evaluated by cross-hatch adhesion test according to ASTM D3359, in which the adhesion of coating films to a paint by applying and removing pressure-sensitive tape over lattice pattern cuts made in the paint
Table 3. Test results for inventive working solutions
Figure PCTCN2018076596-appb-000003
Table 4. Test results for inventive working solutions
Figure PCTCN2018076596-appb-000004
Table 5. Test results for comparative working solutions
Figure PCTCN2018076596-appb-000005
＊N.A. means the working solutions are not applicable and the tests could not be made.
As shown in the Tables 3 and 4, the inventive examples achieved excellent performance in all tests. For instance, as shown in Fig. 1, the appearance of the coated substrate of magnesium alloy treated by the inventive composition of Example 1 exhibited a metallic gloss and silvery color tone. As shown in Fig. 2, the test result of cross-hatch adhesion demonstrated an excellent adhesion of the inventive composition of Example 1 to paint coating. However, the comparative examples are not satisfactory in at least one test item.

Claims (14)

  1. A surface treatment composition for light metallic material, comprising:
    (1) a rare earth element containing compound,
    (2) a silane coupling agent, and
    (3) a polyhydroxyl monocarboxylic acid.
  2. The surface treatment composition for light metallic material according to claim 1, wherein the rare earth element containing compound is selected from tetravalent cerium compounds and trivalent compounds, hydrates and mixture thereof.
  3. The surface treatment composition for light metallic material according to claim 1 or 2, wherein the silane coupling agent having an amino functional group is represented by
    (R 2-O)  3-Si-R 3-NH 2,
    wherein R 2 is an alkyl group containing 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms and most preferably is a methyl group, R 3 is an alkylene moiety containing 1 to 10 carbon atoms optionally substituted with an amine group.
  4. The surface treatment composition for light metallic material according to any of the preceding claims, wherein the silane coupling agent is selected from aminomethylaminopropyltrimethoxylsilane aminopropyltrimethoxysilane, aminopropyltriethoxysilane, and mixture thereof.
  5. The surface treatment composition for light metallic material according to any of the preceding claims, wherein the polyhydroxyl monocarboxylic acid is represented by 
    R 4R 5R 6-COOH,
    wherein, R 4 is alkyl, alkoxyl, aralkyl, or aryl group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH, R 5 and R 6 are each independently alkylene, alkoxylene, aralkylene or arylene group of saturated or unsaturated, isomeric or non-isomeric, straight or branched chain or cyclic form, having 1 to 25 carbon atoms, and optionally substituted by OH, with the proviso that the number of hydroxyl groups in R 4, R 5 and R 6 is two or more, and preferably from 2 to 6.
  6. The surface treatment composition for light metallic material according to any of the preceding claims, wherein the polyhydroxyl monocarboxylic acid is selected from 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, 2, 3, 4, 5, 6, 7-hexahydroxyheptanoic acid, 2, 3, 4, 5, 6, 7, 8-hexahydroxyoctanoic acid, and lactone thereof, and preferably is 2, 3, 4-trihydroxybutanoic acid, 2, 3, 4, 5-tetrahydroxypentanoic acid, 2, 3, 4, 5, 6-pentahydroxyhexanoic acid, lactone, isomer, derivative, and mixture thereof.
  7. The surface treatment composition for light metallic material according to any of the preceding claims, further comprising a salt of polyhydroxyl monocarboxylic acid selected from alkali metal  salt, alkali earth metal salt, aluminum salt, zinc salt, ammonium salt of polyhydroxyl monocarboxylic acid, and mixture thereof.
  8. The surface treatment composition for light metallic material according to any of the preceding claims, wherein the weight ratio of the silane coupling agent to the polyhydroxyl monocarboxylic acid is in the range of 0.5 to 5, preferably 1 to 3.
  9. The surface treatment composition for light metallic material according to any of the preceding claims, wherein the weight ratio of the silane coupling agent to the rare earth element containing compound is in the range of 0.5 to 15, preferably 0.6 to 10.
  10. An aqueous surface treatment solution for light metallic material, comprising the surface treatment composition for light metallic material according to any of the preceding claims and water, in which the pH value of the solution is in the range of 1 to 6.5, preferably 2 to 6.3.
  11. An aqueous surface treatment solution for light metallic material, comprising:
    (1) 0.01%to 0.5%, and preferably from 0.03%to 0.3%of a rare earth element containing compound,
    (2) 0.01%to 0.5%, and preferably from 0.02%to 0.3%of a silane coupling agent, and
    (3) 0.01%to 0.5%, and preferably from 0.03%to 0.4%of a polyhydroxyl monocarboxylic acid,
    (4) 0 to 0.5%, and preferably from 0.03%to 0.3%of a salt of polyhydroxyl monocarboxylic acid, and
    (5) 60%to 99.9%, preferably 80%to 99.9%of water,
    in which the percentage is based on the weight of the aqueous surface treatment solution for light metallic material.
  12. A method for improving corrosion resistance of a metallic substrate, comprising:
    (1) providing the surface treatment composition for light metallic material according to any of claims 1 to 10 or the aqueous surface treatment solution for light metallic material according to claim 11,
    (2) contacting the metallic substrate with the surface treatment composition or the aqueous surface treatment solution for light metallic material, and
    (3) allowing the surface treatment composition for light metallic material to dry to form a coating on the substrate.
  13. An article of manufacture, comprising a conversion coating prepared by the surface treatment composition for light metallic material according to any of claims 1 to 10 or the aqueous surface treatment solution for light metallic material according to claim 11.
  14. The use of the surface treatment composition for light metallic material according to any of claims 1 to 10 or the aqueous surface treatment solution for light metallic material according to claim 11 in improving corrosion resistance of a light metallic substrate.
PCT/CN2018/076596 2018-02-13 2018-02-13 Surface treatment composition for light metallic material WO2019157612A1 (en)

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