EP0765405A1 - Process for forming a phosphate conversion coating - Google Patents

Process for forming a phosphate conversion coating

Info

Publication number
EP0765405A1
EP0765405A1 EP95926607A EP95926607A EP0765405A1 EP 0765405 A1 EP0765405 A1 EP 0765405A1 EP 95926607 A EP95926607 A EP 95926607A EP 95926607 A EP95926607 A EP 95926607A EP 0765405 A1 EP0765405 A1 EP 0765405A1
Authority
EP
European Patent Office
Prior art keywords
conversion coating
fluoride
process according
sludge
cationic polymeric
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95926607A
Other languages
German (de)
French (fr)
Other versions
EP0765405A4 (en
Inventor
Kenji Aizawa
Yutaka Okabayashi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Henkel Corp
Original Assignee
Henkel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henkel Corp filed Critical Henkel Corp
Publication of EP0765405A1 publication Critical patent/EP0765405A1/en
Publication of EP0765405A4 publication Critical patent/EP0765405A4/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • C23C22/34—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 fluorides or complex fluorides
    • C23C22/36—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 fluorides or complex fluorides containing also phosphates
    • C23C22/362—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 fluorides or complex fluorides containing also phosphates containing also zinc cations
    • 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
    • C23C22/73—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 characterised by the process
    • 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
    • C23C22/86—Regeneration of coating baths

Definitions

  • This invention relates to a method for forming a phosphate conversion coating on metal surfaces that include at least some aluminiferous metal surfaces, which for the purposes of the present invention are to be understood as those containing at least 0.5 % of aluminum in their surfaces, are generally exemplified by aluminum sheet, steel sheet plated with Zn-AI alloy, aluminum- plated steel sheet, and the like, and are found, for example, on automotive outer body sheet, on colored sheet-metal roofing material, and so forth.
  • Phosphate conversion coating of metals forms on the metal surface a coating, with a chemical composition typified by Zn 3 (P0 4 ) 2 *nH 2 0, Zn 2 Fe(P0 4 ) 2 * > n H 2 0, and/or Zn 2 Ca(P0 4 ) 2 «> nH 2 0 for the example of zinc phos ⁇ phate treatments.
  • This is brought about by contacting the metal surface, usually by spraying or dipping, with a phosphate liquid conversion coating composition in order to dissolve the surface of the metal.
  • Phosphate conversion coatings im ⁇ prove the metal's resistance to rusting and its paint adherence.
  • Zinc phosphate liquid conversion coating compositions contain phosphoric acid, Zn 2+ ions, and water as their essential components and may contain, for ex- ample, Ni 2+ , Mn 2+ , Ca 2+ , Fe 2+ , H + , Na + , K + , NH 4 + , N0 3 " , NO/, fluoride (which may be simple fluoride and/or complex fluorides such as fluozirocnate, fluosilicate, fluoborate, and the like), S0 4 2" , Cl " , or the like, as optional components.
  • the list ⁇ ed components represent those in general use for phosphate liquid conversion coating compositions.
  • Phosphate sludge i.e., FeP0 4 » n H 2 0, Zn 3 (P0 4 ) 2 * n H 2 0, etc.
  • Sludge-eliminating measures such as filtration and sedimentation are therefore ordinarily used since a low sludge content in the liquid conversion coating composition is desirable for forming phosphate conversion coatings.
  • Zn-AI alloy-plated steel sheet exhibits a better corrosion resistance and heat resistance than ordinary Zn-plated steel sheet, and as a result its applica ⁇ tions as a corrosion-resistant material have in recent years been undergoing act ⁇ ive development.
  • steel sheet plated with Zn containing approxi ⁇ mately 5 % of aluminum is widely used where painting is to be executed on the steel sheet.
  • this type of steel sheet is subjected to phosphate conversion coating, aluminum ions accumulate in the treatment bath. Removal of aluminum ions from the reaction system is desired because aluminum ions are unnecessary and in fact detrimental to phosphate conversion coating.
  • a sludge such as Nal AIFg, NasAIFg, etc., may also be deliberately produced, in addition to the phosphate sludge which arises spontaneously during conversion coating of any ferrous and/or zinciferous surface.
  • the term "sludge” designates a mixture of (a) solids, such as the phos ⁇ phates and aluminum compounds produced by the reactions occurring during phosphate conversion coating of the metal or produced by the addition of NaHF 2 , KHF 2 , etc., plus (b) small amounts of metal salts not due to the aforesaid reac- tions, plus (c) atmospheric dust and entrained contamination adhering on the metal.
  • This sludge is therefore typically a mixture of components such as zinc phosphate, iron phosphate, aluminum compounds such as cryolite (Na 3 AIF 6 ) or elpasolite (Naf AIFg), entrained contaminants, dust, and the like.
  • Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 57-70281 [70,281/1982] discloses a phosphate conversion coating method that maintains the Al ion concentration in a zinc phosphate liquid conversion coating composition at 50 parts per million (hereinafter usually abbreviated "ppm") or less.
  • the Al elution into a zinc phosphate liquid conversion coating composition is 0.2 x 10 "3 to 1.0 x 10 "3 moles per square meter, herein ⁇ after usually abbreviated as "mol/m 2 ".
  • the prescribed Al ion concentration is ob ⁇ tained in this method by the precipitative removal of Al from the reaction system as elpasolite (NaKzAIFe).
  • Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 60-204889 [204,889/1985] discloses a phosphate conversion coating meth ⁇ od that is directed to zinc phosphate conversion coating liquid compositions whose principal ingredients are 0.85 to 1.7 grams per liter (hereinafter usually ab- breviated as "g/L") of Zn ions, 1.0 to 2.5 g/L of Ni ions, 5.5 to 10 g/L of P0 4 ions, 0.8 to 1.5 g/L of N0 3 ions, 1.3 to 5.5 g/L of F ions, and small quantities of addit ⁇ ives.
  • g/L grams per liter
  • NaHF 2 and KHF 2 — or NaHF 2 and KF — are intermittently added to such liquid compositions in a quantity no more than equimolar with the quantity of Al in the liquid conversion coating composition.
  • Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 56-105485 [105,485/1981] teaches a method that facilitates sludge filtration.
  • a polymeric coagulant is added to the conversion coating liquid composition in the phosphate conversion coating of cold-rolled steel sheet.
  • the addition of this polymeric coagulant improves the sedimentability of the phos ⁇ phate compound-containing sludge.
  • this method was not investigated with regard to the sedimentation of aluminum compound-containing sludge.
  • One object of the present invention is to solve the quality and mainte ⁇ nance problems during phosphate conversion coatings, by prior art methods, that are caused by aluminum compound-containing sludges, especially the problems noted above.
  • percent, "parts of, and ratio values are by weight;
  • the term “polymer” includes “oligomer”, “copolymer”, “terpolymer”, and the like;
  • the first definition or description of the meaning of a word, phrase, acro- nym, abbreviation or the like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or the like and applies, mutatis mutandis, to nor ⁇ mal grammatical variations thereof;
  • the description of a group or class of mater ⁇ ials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred;
  • specification of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the com ⁇ position as a whole; and any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counter
  • Aluminum compound-containing sludge at some point becomes suspend ⁇ ed in the liquid conversion coating composition during processes that remove Al ions — which can prevent formation of the phosphate conversion coating — from the reaction system, and, since aluminum compound-containing sludge has a low sedimentability, it gradually accumulates in the liquid conversion coating composition.
  • Aluminum compound-containing sludge is more soluble in water than other phosphate-based sludges; therefore, the former is more easily dis ⁇ solved by the moisture permeating through paint films.
  • the invention applies to the use of a phosphate conversion coating liquid composition that contains fluoride, in addition to the essential components listed above (phosphoric acid, zinc, and water).
  • the fluoride is desired for its good etching activity on aluminiferous surfaces, which is necessary for the production of the best quality phosphate films on aluminiferous metals.
  • the essence of the invention is the use of at least one cationic coagulant to cause coagulation and sedimentation of sludge suspended in a fluoride-containing phosphate conver ⁇ sion coating liquid composition, in which at least part of the sludge includes alum- inum compounds.
  • cationic polymeric coagulant is able to prevent quality deterioration during prolonged use of the same volume of phosphating liquid composition, by preventing substantial contact between the aluminum compound-containing sludge and the conversion coated workpiece.
  • the inventors obtained the following information from experiments into a means by which polymeric coagulant(s) would be able to induce the coagulation, enlargement, and sedimentation of each sludge component present in a fluoride- containing phosphate conversion coating liquid composition.
  • the addition of the cationic polymeric coagulant first is pre- ferred.
  • the cationic coagulant whose addition is necessary to induce coagulation and en ⁇ largement—is preferably added in a quantity at least as large as that of the anionic coagulant.
  • the aluminum compound- free sludge is first coagulated and sedimented using an anionic polymeric coagulant, a condition is produced in which aluminum compound-contain ⁇ ing sludge is suspended in the liquid conversion coating composition.
  • the cationic polymeric coagulant When the cationic polymeric coagulant is then added to liquid conversion coating composition in this state, it is preferably added in a quantity at least as large as the addition of anionic coagulant.
  • the method for introducing the cationic coagulant into the phosphate liquid conversion coating composition is not critical to the present invention, and any method may be used that establishes the presence of the cationic coagulant in the liquid conversion coating composition. Preferred specific methodologies are (1) replenishment with a base or secondary ingredient to which the cationic coagulant has been preliminarily added, and (2) addition of an aqueous solution prepared by dilution of the cationic coagulant in phosphate liquid conversion coating composition.
  • the cationic coagulant should as a general rule be used at a concentra ⁇ tion of 1 to 100 ppm, and preferably 2 to 10 ppm. Within these ranges, the opti ⁇ mum concentration is more or less determined by the content and particle size of the sludge.
  • the cationic coagulant has a reduced effect at a concentration be- low 1 ppm, while concentrations exceeding 100 ppm are economically undesir ⁇ able.
  • the cationic polymeric coagulant may have a strong, moderate, or weak ionic strength, be ⁇ cause all of these are effective and practical.
  • the molecular weight of the cation ⁇ ic polymeric coagulant is preferably 1*10 5 to 2*10 7 .
  • the suspended sludge concentration prior to addition of the cationic poly- meric coagulant is not narrowly limited for the present invention, but as a general rule will be 100 to 10,000 ppm, assuming treatment in existing continuous con ⁇ version coating lines.
  • the proportion of aluminum compound-containing sludge in this concentration increases with elapsed treatment time and in some cases may reach as high as 50 % of the total sludge, or 5,000 ppm, based on the entire phosphating liquid composition.
  • Either of the above-described addition methods (1) and (2) can reduce the suspended sludge concentration to 0.1 to 10 ppm within a few minutes after coagulant addition.
  • Nonionic coagulant or anionic coagulant may also be added on an option ⁇ al basis in the execution of the present invention in order to sediment sludge other than aluminum compound-containing sludge.
  • test liquid conversion coating composition was prepared as follows: First, Al sheet and cold-rolled steel sheet were subjected to zinc phosphate con ⁇ version coating to give approximately 100 ppm of Al ions and approximately 2,000 ppm of phosphate sludge in the liquid conversion coating composition. After this, aluminum compound-containing sludge was produced by adding a co ⁇ agulant, thus yielding the test liquid conversion coating composition. The evalu ⁇ ations were conducted by the methods described below.
  • Aluminum sheet was treated using liquid conversion coating composition obtained by the addition of coagulant to test liquid conversion coating composi ⁇ tion. The status of the coating was then visually inspected. ⁇ 4 ⁇ Water-resistant secondary adherence Aluminum sheet was treated with test liquid conversion coating composi ⁇ tion and then rinsed with water and dried. This was followed by cationic electro- deposition of a base protective coating, an intermediate coating, and a top coat- ing, in each case equivalent to automotive applications, to give the test coupon. After the test coupon had been immersed for 240 hours in deionized water at 40 °C, a Crosshatch pattern (2 x 2 mm, 100 squares) was scribed down to the alum ⁇ inum sheet. An adherence test was then conducted by tape peeling. Test liquid conversion coating composition

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)

Abstract

To prevent the deterioration in water-resistant secondary adherence that occurs during prolonged use of a fluoride-containing phosphate conversion coating liquid composition to form a conversion coating on metal surfaces that are at least partly aluminiferous, the aluminum compound-containing sludge produced in the phosphate conversion coating liquid composition as it is used is coagulated and sedimented by adding at least one cationic polymeric coagulant to the sludge-containing phosphate conversion coating liquid composition.

Description

Description PROCESS FOR FORMING A PHOSPHATE CONVERSION COATING
BACKGROUND OF THE INVENTION Field of the Invention
This invention relates to a method for forming a phosphate conversion coating on metal surfaces that include at least some aluminiferous metal surfaces, which for the purposes of the present invention are to be understood as those containing at least 0.5 % of aluminum in their surfaces, are generally exemplified by aluminum sheet, steel sheet plated with Zn-AI alloy, aluminum- plated steel sheet, and the like, and are found, for example, on automotive outer body sheet, on colored sheet-metal roofing material, and so forth. Statement of Related Art
Phosphate conversion coating of metals forms on the metal surface a coating, with a chemical composition typified by Zn3(P04)2*nH20, Zn2Fe(P04)2*>n H20, and/or Zn2Ca(P04)2 «>nH20 for the example of zinc phos¬ phate treatments. This is brought about by contacting the metal surface, usually by spraying or dipping, with a phosphate liquid conversion coating composition in order to dissolve the surface of the metal. Phosphate conversion coatings im¬ prove the metal's resistance to rusting and its paint adherence.
Zinc phosphate liquid conversion coating compositions contain phosphoric acid, Zn2+ ions, and water as their essential components and may contain, for ex- ample, Ni2+, Mn2+, Ca2+, Fe2+, H+, Na+, K+, NH4 +, N03 ", NO/, fluoride (which may be simple fluoride and/or complex fluorides such as fluozirocnate, fluosilicate, fluoborate, and the like), S04 2", Cl", or the like, as optional components. The list¬ ed components represent those in general use for phosphate liquid conversion coating compositions. Phosphate sludge, i.e., FeP04 »n H20, Zn3(P04)2* n H20, etc., is produced during the phosphate conversion coating of metal surfaces. Sludge-eliminating measures such as filtration and sedimentation are therefore ordinarily used since a low sludge content in the liquid conversion coating composition is desirable for forming phosphate conversion coatings. Zn-AI alloy-plated steel sheet exhibits a better corrosion resistance and heat resistance than ordinary Zn-plated steel sheet, and as a result its applica¬ tions as a corrosion-resistant material have in recent years been undergoing act¬ ive development. In particular, steel sheet plated with Zn containing approxi¬ mately 5 % of aluminum is widely used where painting is to be executed on the steel sheet. However, when this type of steel sheet is subjected to phosphate conversion coating, aluminum ions accumulate in the treatment bath. Removal of aluminum ions from the reaction system is desired because aluminum ions are unnecessary and in fact detrimental to phosphate conversion coating.
In order to prevent Al ion accumulation in the liquid conversion coating composition, it is desirable in the conversion coating of aluminiferous metal sur¬ faces to remove Al ions from the reaction system as a solid. For this purpose, when conversion coating at least partially aluminiferous metal surfaces, a sludge such as Nal AIFg, NasAIFg, etc., may also be deliberately produced, in addition to the phosphate sludge which arises spontaneously during conversion coating of any ferrous and/or zinciferous surface. For the purposes of the present speci¬ fication, the term "sludge" designates a mixture of (a) solids, such as the phos¬ phates and aluminum compounds produced by the reactions occurring during phosphate conversion coating of the metal or produced by the addition of NaHF2, KHF2, etc., plus (b) small amounts of metal salts not due to the aforesaid reac- tions, plus (c) atmospheric dust and entrained contamination adhering on the metal. This sludge is therefore typically a mixture of components such as zinc phosphate, iron phosphate, aluminum compounds such as cryolite (Na3AIF6) or elpasolite (Naf AIFg), entrained contaminants, dust, and the like.
Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 57-70281 [70,281/1982] discloses a phosphate conversion coating method that maintains the Al ion concentration in a zinc phosphate liquid conversion coating composition at 50 parts per million (hereinafter usually abbreviated "ppm") or less. According to this disclosure, the Al elution into a zinc phosphate liquid conversion coating composition, expressed on the basis of the unit surface area of the steel sheet, is 0.2 x 10"3 to 1.0 x 10"3 moles per square meter, herein¬ after usually abbreviated as "mol/m2". According to this method, at this quantity of elution the Al ion can be maintained at 50 ppm or less by removal of the Al as a precipitate through the continuous supply of NaHF2 equimolar with the eluting Al (= 0.2 x 103 to 1.0 x 10"3 mol/m2) and KHF2 at twice the moles of the eluting Al (= 0.4 x 10"3 to 2.0 x 10"3 mol/m2). The prescribed Al ion concentration is ob¬ tained in this method by the precipitative removal of Al from the reaction system as elpasolite (NaKzAIFe).
Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 60-204889 [204,889/1985] discloses a phosphate conversion coating meth¬ od that is directed to zinc phosphate conversion coating liquid compositions whose principal ingredients are 0.85 to 1.7 grams per liter (hereinafter usually ab- breviated as "g/L") of Zn ions, 1.0 to 2.5 g/L of Ni ions, 5.5 to 10 g/L of P04 ions, 0.8 to 1.5 g/L of N03 ions, 1.3 to 5.5 g/L of F ions, and small quantities of addit¬ ives. In this method, NaHF2 and KHF2 — or NaHF2 and KF — are intermittently added to such liquid compositions in a quantity no more than equimolar with the quantity of Al in the liquid conversion coating composition. This results in the sedimentative removal of the Al in the zinc phosphate liquid conversion coating composition as K2NaAIF6 and provides control of the Al ions concentration in the liquid conversion coating composition to 500 ppm or less.
Removal of the aluminum ions eluted from zinc-aluminum alloy plating during phosphate conversion coating as cryolite (Na3AIF6) is also known and is described in Dai-39-kai Fushoku Boshoku Toronkai Gaiyo [Title in English: Pro¬ ceedings of the 39th Japan Corrosion Conference] in Fushoku Boshoku Kyokai- shi [Title in English: Corrosion Engineering].
Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 56-105485 [105,485/1981] teaches a method that facilitates sludge filtration. In this method, a polymeric coagulant is added to the conversion coating liquid composition in the phosphate conversion coating of cold-rolled steel sheet. The addition of this polymeric coagulant improves the sedimentability of the phos¬ phate compound-containing sludge. However, this method was not investigated with regard to the sedimentation of aluminum compound-containing sludge. The sedimentation of zinc phosphate-based sludge is facilitated by the ad¬ dition of polymeric coagulant in the method taught in Japanese Patent Applica¬ tion Laid Open [Kokai or Unexamined] Number Sho 56-105485 for the formation of zinc phosphate conversion coatings on steel sheet or zinc-plated steel sheet. However, there are believed to have been no previous investigations into a meth¬ od that could induce the sedimentation of sludge from a liquid conversion coating composition in which aluminum compounds are present. DESCRIPTION OF THE INVENTION
Object of the Invention - Problems To Be Solved
One object of the present invention is to solve the quality and mainte¬ nance problems during phosphate conversion coatings, by prior art methods, that are caused by aluminum compound-containing sludges, especially the problems noted above.
General Principles of Description
Except in the claims and the specific examples, or where otherwise ex¬ pressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, unless expressly stated to the contrary: percent, "parts of, and ratio values are by weight; the term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the first definition or description of the meaning of a word, phrase, acro- nym, abbreviation or the like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or the like and applies, mutatis mutandis, to nor¬ mal grammatical variations thereof; the description of a group or class of mater¬ ials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; specification of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the com¬ position as a whole; and any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to the objects of the invention. Summary of the Invention
In phosphate conversion coating, the solids produced in association with the reactions and film formation as a general rule have a very small particle size when produced, but gradually aggregate and grow and become increasingly easy to filter. However, this phenomenon varies substantially as a function of the particular compounds making up the sludge. It has been found that aluminum- free phosphate sludges undergo aggregation and sedimentation relatively read¬ ily, but that the aluminum fluorides and NagAIFg resist aggregation and enlargement. These aluminum fluorides were found to remain suspended in the phosphate conversion coating liquid composition in the small particle size form without change, thus making them refractory to filtration and sedimentation. Aluminum compound-containing sludge at some point becomes suspend¬ ed in the liquid conversion coating composition during processes that remove Al ions — which can prevent formation of the phosphate conversion coating — from the reaction system, and, since aluminum compound-containing sludge has a low sedimentability, it gradually accumulates in the liquid conversion coating composition. Aluminum compound-containing sludge is more soluble in water than other phosphate-based sludges; therefore, the former is more easily dis¬ solved by the moisture permeating through paint films. It is believed that, when phosphating is done by use of zinc phosphating liquid composition containing substantial amounts of suspended aluminum compound-containing sludge, some of the aluminum compound-containing sludge codeposits in an intimate mixture with and/or on the surface of the depositing phosphate conversion coating and that this is the cause of the quality deteriorations in phosphate conversion coatings.
Filtration by continuous or intermittent forced passage of the liquid conver- sion coating composition through a suitable partially permeable barrier could be contemplated as a means for preventing the quality degradation caused by alum¬ inum compound-containing sludge. However, the forced filtration of aluminum compound-containing sludge is quite difficult.
The invention applies to the use of a phosphate conversion coating liquid composition that contains fluoride, in addition to the essential components listed above (phosphoric acid, zinc, and water). The fluoride is desired for its good etching activity on aluminiferous surfaces, which is necessary for the production of the best quality phosphate films on aluminiferous metals. The essence of the invention is the use of at least one cationic coagulant to cause coagulation and sedimentation of sludge suspended in a fluoride-containing phosphate conver¬ sion coating liquid composition, in which at least part of the sludge includes alum- inum compounds. The use of cationic polymeric coagulant according to the present invention is able to prevent quality deterioration during prolonged use of the same volume of phosphating liquid composition, by preventing substantial contact between the aluminum compound-containing sludge and the conversion coated workpiece. Detailed Description of the Invention. Including Preferred Embodiments
The inventors obtained the following information from experiments into a means by which polymeric coagulant(s) would be able to induce the coagulation, enlargement, and sedimentation of each sludge component present in a fluoride- containing phosphate conversion coating liquid composition. (a) Aluminum compound-containing sludges are presumably negatively charged since they are coagulated and sedimented by cationic polymeric coagulants.
(b) The entire mixed sludge is coagulated and sedimented when a cationic polymeric coagulant is added to a liquid conversion coating composition in which a mixed sludge (aluminum compound and phosphate) is sus¬ pended. The coagulation and sedimentation of only the phosphate-based sludge does not occur.
(c) In the case of co-use of anionic polymeric coagulant and cationic polymer¬ ic coagulant, the addition of the cationic polymeric coagulant first is pre- ferred. For example, when anionic coagulant is added first, the cationic coagulant — whose addition is necessary to induce coagulation and en¬ largement—is preferably added in a quantity at least as large as that of the anionic coagulant. In specific terms, when the aluminum compound- free sludge is first coagulated and sedimented using an anionic polymeric coagulant, a condition is produced in which aluminum compound-contain¬ ing sludge is suspended in the liquid conversion coating composition. When the cationic polymeric coagulant is then added to liquid conversion coating composition in this state, it is preferably added in a quantity at least as large as the addition of anionic coagulant. The method for introducing the cationic coagulant into the phosphate liquid conversion coating composition is not critical to the present invention, and any method may be used that establishes the presence of the cationic coagulant in the liquid conversion coating composition. Preferred specific methodologies are (1) replenishment with a base or secondary ingredient to which the cationic coagulant has been preliminarily added, and (2) addition of an aqueous solution prepared by dilution of the cationic coagulant in phosphate liquid conversion coating composition.
The cationic coagulant should as a general rule be used at a concentra¬ tion of 1 to 100 ppm, and preferably 2 to 10 ppm. Within these ranges, the opti¬ mum concentration is more or less determined by the content and particle size of the sludge. The cationic coagulant has a reduced effect at a concentration be- low 1 ppm, while concentrations exceeding 100 ppm are economically undesir¬ able.
There are no narrow limitations placed on the cationic polymeric coagulant itself, although the use of polymers with polyacrylic ester or polyacrylamide back¬ bones and cationic, usually amine or quaternary ammonium, moieties in side groups chemically attached to the polymer backbones is preferred. The cationic polymeric coagulant may have a strong, moderate, or weak ionic strength, be¬ cause all of these are effective and practical. The molecular weight of the cation¬ ic polymeric coagulant is preferably 1*105 to 2*107.
The suspended sludge concentration prior to addition of the cationic poly- meric coagulant is not narrowly limited for the present invention, but as a general rule will be 100 to 10,000 ppm, assuming treatment in existing continuous con¬ version coating lines. The proportion of aluminum compound-containing sludge in this concentration increases with elapsed treatment time and in some cases may reach as high as 50 % of the total sludge, or 5,000 ppm, based on the entire phosphating liquid composition. Either of the above-described addition methods (1) and (2) can reduce the suspended sludge concentration to 0.1 to 10 ppm within a few minutes after coagulant addition. Nonionic coagulant or anionic coagulant may also be added on an option¬ al basis in the execution of the present invention in order to sediment sludge other than aluminum compound-containing sludge.
The invention is explained in greater detail below using working examples, and the benefits of the invention are illustrated by comparative examples. Examples
The test liquid conversion coating composition was prepared as follows: First, Al sheet and cold-rolled steel sheet were subjected to zinc phosphate con¬ version coating to give approximately 100 ppm of Al ions and approximately 2,000 ppm of phosphate sludge in the liquid conversion coating composition. After this, aluminum compound-containing sludge was produced by adding a co¬ agulant, thus yielding the test liquid conversion coating composition. The evalu¬ ations were conducted by the methods described below.
Evaluation Methods £1} Coagulation and sedimentation performance
The polymeric coagulant (see below) was added to test liquid conversion coating composition followed by stirring for 1 minute and standing for 2 minutes. Coagulation and enlargement of the sludge and the clarity of the supernatant liquid were then inspected visually. (2) Filtration performance
Test liquid conversion coating composition and liquid conversion coating composition after polymeric coagulant addition (see below) were filtered using nonwoven fabric with an air permeability of 100. The clarity of the filtrate was then inspected visually. (3) Conversion performance
Aluminum sheet was treated using liquid conversion coating composition obtained by the addition of coagulant to test liquid conversion coating composi¬ tion. The status of the coating was then visually inspected. {4} Water-resistant secondary adherence Aluminum sheet was treated with test liquid conversion coating composi¬ tion and then rinsed with water and dried. This was followed by cationic electro- deposition of a base protective coating, an intermediate coating, and a top coat- ing, in each case equivalent to automotive applications, to give the test coupon. After the test coupon had been immersed for 240 hours in deionized water at 40 °C, a Crosshatch pattern (2 x 2 mm, 100 squares) was scribed down to the alum¬ inum sheet. An adherence test was then conducted by tape peeling. Test liquid conversion coating composition
Zn2+ 1.5 g/L
Ni2+ 0.5 g/L
PCλ,3" 13.5 g/L fluoride 1.0 g/L (stoichiometric equivalent as fluorine atoms)
N03 " 6.0 g/L
NOy 0.1 g/L
Na+ 1.5 g/L
Na3AIF6 800 ppm (as sludge)
FeP04 2000 ppm (as sludge)
PH 2.9
Test polymeric coagulants (from Sanyo Chemical Industries Company, Ltd.):
Identifier Coagulant Trade Name lonicitv
A Sanflock™ AM-170P Anionic
N Sanflock™ N-500P Nonionic
C1 Sanflock™ C-009P Strongly cationic
C2 Sanflock™ CE-682P Weakly cationic
Evaluation Scales
(1) Coagulation and sedimentation performance
+ the sludge was substantially coagulated and enlarged, and the supernatant had either become clear or exhibited a small residual turbidity x the entire liquid composition lacked transparency
(2) Filtration performance
+ almost completely filtered x transparency not obtained, small quantity of filtrate (3) Conversion performance
+ a good quality coating was obtained x the coating was nonuniform and uncoated areas were present (4) Water-resistant secondary adherence + no peeled squares less than 10 peeled squares 10 or more peeled squares
Additional test conditions and results are shown in Table 1 below. In Ex- ample 5, 4 mg/L of coagulant C2 was first added with stirring followed by the ad¬ dition of 2 mg/L of coagulant A with stirring. In Example 6, 4 mg/L of coagulant C2 was first added with stirring followed by the addition of 2 mg/L of coagulant N with stirring. In Example 7, 2 mg/L of coagulant A was first added with stirring followed by the addition of 4 mg/L of coagulant C2 with stirring. While phosphate conversion coating itself was possible in the comparative examples, poor ratings were obtained in the comparative examples for the coag¬ ulation and sedimentation performance, filtration performance, and water-resist¬ ant secondary adherence. By preventing contact between the metal treatment workpiece and most of the aluminum compound-containing sludge, the method according to the instant invention is able to prevent deterioration in the quality of phosphate conversion coatings.
TABLE 1
Example Coagulant Test Results ("Ex") or Com¬ parison
Example Ident¬ Concen¬ Coagula¬ Filtra¬ Conver¬ Water- ("CE") ifier tration, tion and tion sion resistant
Number ppm Sedimen¬ Per¬ Per¬ Secon¬ tation Per¬ form¬ form¬ dary formance ance ance Adhesion
Ex l C2 2 + + + +
Ex 2 C2 100 + + + +
Ex 3 Cl 2 + + + +
Ex 4 Cl 100 + + + +
Ex 5 C2 + A 6 + + + +
Ex 6 C2 + N 6 + + + +
Ex 7 A + C2 6 + + + +
CE 1 none 0 x x + x
CE 2 A 20 x x + X
CE 3 N 20 x x + x

Claims

1. A process for forming a phosphate conversion coating on metal surfaces that include at least some aluminiferous metal surface by contacting the metal surfaces with a volume of fluoride-containing phosphate conversion coating liquid composition for a sufficient time at a sufficient temperature to cause: (i) formation of a conversion coating on the metal surfaces and (ii) generation of insoluble dis¬ persed solid sludge in the volume of fluoride-containing phosphate conversion coating liquid composition, said dispersed solid sludge including aluminum com¬ pounds, wherein the improvement comprises adding to the volume of fluoride- containing phosphate conversion coating liquid composition an amount of at least one cationic polymeric coagulant that is sufficient to cause coagulation and sedi¬ mentation of at least part of the aluminum compound-containing dispersed sludge.
2. A process according to claim 1 , wherein the amount of cationic polymeric coagulant added to the volume of fluoride-containing phosphate conversion coat¬ ing liquid composition results in a concentration from about 1 to about 100 ppm of cationic polymeric coagulant in the fluoride-containing phosphate conversion coating liquid composition.
3. A process according to claim 2, wherein the concentration of cationic polymeric coagulant in the fluoride-containing phosphate conversion coating liquid composition is from about 2 to about 10 ppm.
4. A process according to claim 3, wherein the total concentration of dispersed sludge in the fluoride-containing phosphate conversion coating liquid composition before addition of cationic polymeric coagulant is from about 100 to about 10,000 ppm.
5. A process according to claim 4, wherein the total concentration of dis¬ persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu¬ lant is reduced to a value in the range from about 0.1 to about 10 ppm.
6. A process according to claim 5, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1 105 to about 2x107.
7. A process according to claim 1 , wherein the concentration of cationic polymeric coagulant in the fluoride-containing phosphate conversion coating liquid composition is from about 2 to about 10 ppm.
8. A process according to claim 7, wherein the total concentration of dis- persed sludge in the fluoride-containing phosphate conversion coating liquid composition before addition of cationic polymeric coagulant is from about 100 to about 10,000 ppm.
9. A process according to claim 8, wherein the total concentration of dis¬ persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu¬ lant is reduced to a value in the range from about 0.1 to about 10 ppm.
10. A process according to claim 9, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1*105 to about 2χ107.
11. A process according to claim 2, wherein the total concentration of dispersed sludge in the fluoride-containing phosphate conversion coating liquid composition before addition of cationic polymeric coagulant is from about 100 to about 10,000 ppm.
12. A process according to claim 11 , wherein the total concentration of dis¬ persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu¬ lant is reduced to a value in the range from about 0.1 to about 10 ppm.
13. A process according to claim 12, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1 105 to about 2χ107.
14. A process according to claim 1 , wherein the total concentration of dispersed sludge in the fluoride-containing phosphate conversion coating liquid composition before addition of cationic polymeric coagulant is from about 100 to about 10,000 ppm.
15. A process according to claim 14, wherein the total concentration of dis¬ persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu- lant is reduced to a value in the range from about 0.1 to about 10 ppm.
16. A process according to claim 15, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1 10s to about 2x107.
17. A process according to claim 3, wherein the total concentration of dis- persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu¬ lant is reduced to a value in the range from about 0.1 to about 10 ppm.
18. A process according to claim 17, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1χ105 to about 2x107.
19. A process according to claim 2, wherein the total concentration of dis¬ persed sludge in the fluoride-containing phosphate conversion coating liquid composition within a few minutes after addition of the cationic polymeric coagu¬ lant is reduced to a value in the range from about 0.1 to about 10 ppm.
20. A process according to claim 19, wherein the molecular weight of the cationic polymeric coagulant is in the range from about 1 χ105 to about 2x107.
EP95926607A 1994-07-12 1995-07-11 Process for forming a phosphate conversion coating Withdrawn EP0765405A4 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP15990194A JPH0820876A (en) 1994-07-12 1994-07-12 Phosphate chemical conversion treatment
JP159901/94 1994-07-12
PCT/US1995/008228 WO1996001914A1 (en) 1994-07-12 1995-07-11 Process for forming a phosphate conversion coating

Publications (2)

Publication Number Publication Date
EP0765405A1 true EP0765405A1 (en) 1997-04-02
EP0765405A4 EP0765405A4 (en) 1997-06-04

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CA (1) CA2194910A1 (en)
WO (1) WO1996001914A1 (en)

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Publication number Priority date Publication date Assignee Title
KR100317680B1 (en) * 1999-04-29 2001-12-22 이계안 Surface treatment agent for treating aluminium alloy and steel plate simultaneously before painting
AU2002237525B2 (en) 2001-02-26 2005-03-10 Nippon Steel Corporation Surface treated steel product, method for production thereof and chemical conversion treatment solution
JP4815072B2 (en) * 2001-07-31 2011-11-16 日本ペイント株式会社 Sludge concentration method, concentrated sludge obtained by this method, and sludge concentration device
EP1521863B1 (en) 2002-07-10 2008-06-25 Chemetall GmbH Method for coating metallic surfaces

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS53109871A (en) * 1977-03-07 1978-09-26 Nippon Paint Co Ltd Treating method for sludge by-product formed in chemical treatment of zinc phosphate film
JPS56105485A (en) * 1980-01-24 1981-08-21 Nippon Parkerizing Co Ltd Chemical conversion process for phosphate coating
JPS5770281A (en) * 1980-10-20 1982-04-30 Nisshin Steel Co Ltd Zinc phosphate treatment of zinc hot dipping steel plate
JPS60204889A (en) * 1984-03-29 1985-10-16 Nisshin Steel Co Ltd Zinc phosphate treatment of steel sheet plated with zn-al alloy
EP0434358A2 (en) * 1989-12-19 1991-06-26 Nippon Paint Co., Ltd. Method for phosphating metal surface with zinc phosphate

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS53109871A (en) * 1977-03-07 1978-09-26 Nippon Paint Co Ltd Treating method for sludge by-product formed in chemical treatment of zinc phosphate film
JPS56105485A (en) * 1980-01-24 1981-08-21 Nippon Parkerizing Co Ltd Chemical conversion process for phosphate coating
JPS5770281A (en) * 1980-10-20 1982-04-30 Nisshin Steel Co Ltd Zinc phosphate treatment of zinc hot dipping steel plate
JPS60204889A (en) * 1984-03-29 1985-10-16 Nisshin Steel Co Ltd Zinc phosphate treatment of steel sheet plated with zn-al alloy
EP0434358A2 (en) * 1989-12-19 1991-06-26 Nippon Paint Co., Ltd. Method for phosphating metal surface with zinc phosphate

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 002, no. 144 (C-029), 30 November 1978 & JP 53 109871 A (NIPPON PAINT CO LTD), 26 September 1978, *
PATENT ABSTRACTS OF JAPAN vol. 005, no. 180 (C-079), 19 November 1981 & JP 56 105485 A (NIPPON PARKERIZING CO LTD), 21 August 1981, *
PATENT ABSTRACTS OF JAPAN vol. 006, no. 149 (C-118), 10 August 1982 & JP 57 070281 A (NISSHIN STEEL CO LTD), 30 April 1982, *
PATENT ABSTRACTS OF JAPAN vol. 010, no. 067 (C-333), 15 March 1986 & JP 60 204889 A (NITSUSHIN SEIKOU KK), 16 October 1985, *
See also references of WO9601914A1 *

Also Published As

Publication number Publication date
WO1996001914A1 (en) 1996-01-25
JPH0820876A (en) 1996-01-23
EP0765405A4 (en) 1997-06-04
CA2194910A1 (en) 1996-01-25

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