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
  • C23C22/361—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 titanium, zirconium or hafnium compounds

Definitions

• This invention relates to a surface treatment composition and process that form a conversion coating on the surface of aluminiferous metals that imparts an excellent corrosion resistance and paint adherence to such surfaces prior to their painting.
• the aqueous solutions of this composition are transparent solutions that resist the production of a precipitating solid even when they contain eluted aluminum.
• the present invention is applied with particularly good effect to the surface treatment of drawn-and-ironed aluminum cans (hereinafter usually abbreviated as "aluminum Dl cans").
• the outside bottom surface of aluminum Dl cans is subjected to high-tem ⁇ perature sterilization without being painted. If this region has a low corrosion resistance, the aluminum is oxidized and blackened during this step, and its appearance is thereby impaired. This phenomenon is generally known as "blackening". As a result, the (unpainted) conversion coating produced by sur ⁇ face treatment desirably should have an intrinsically high corrosion resistance.
• the surface treatment of aluminum Dl cans is carried out mainly using Cr(VI)-containing phosphoric acid-chromate treatments and zirconium-type nonchromate treatments.
• nonchromate surface treatment baths A typical example of nonchromate surface treatment baths is disclosed in Japanese Patent Publication Number Sho 56-33468 [33,468/1981].
• This surface treatment bath is an acidic (pH 1.5 to 4.0) water-based coating solution that contains phosphate, fluoride, and zirconium or titanium or a mixture thereof.
• the characteristic features of this acidic nonchromate treatment bath are s that it contains effective fluoride and does not contain a solid-producing com ⁇ ponent that is prone to precipitation. Since this nonchromate treatment bath does not contain toxic hexavalent chromium, it has come to be widely used at the present time as a surface treatment agent for aluminum Dl cans. However, this bath in actuality also suffers from major drawbacks as described in the following.
• the prior art surface treatment baths are used on can manufacturing lines, they are ordinarily sprayed on the aluminum Dl cans for about 15 to 30 seconds.
• the resulting coating may not be uniform, because of differences that occur between different regions of the can s in the bath flow rate and in the contact conditions between the bath and the surface of the substrate. This creates variations or instabilities in the anticor- rosion performance.
• the present invention seeks to solve the problems described above for the prior art.
• the present invention introduces a bath and a pro- cess using said bath that not only are able to produce a highly corrosion-re ⁇ sistant, strongly paint-adherent conversion coating on the surfaces of alumin ⁇ iferous metal substrates, but which also exhibit excellent properties in terms of conversion coating uniformity, sludging inhibition, and process stability.
• a treatment bath that maintains a transparent appearance can be obtained when an oxidizing agent and a hydrogen fluoride-generating compound that produces a particular value for the HF concentration are also present in a surface treatment bath that contains a phosphoric acid compound and zirconium compound and has a pH of 1.5 to 4.0;
• an excellent corrosion resistance and good paint adherence can be imparted to the surface of aluminiferous metal substrates by the formation thereon of a conversion coating by contacting the surface of the aluminiferous metal with the aforesaid conversion bath for 0.5 to 60 seconds; and (hi) the conversion coating thereby formed is very uniform, while at the same time an excellent sludging inhibition is obtained.
• the highly sludging-inhibited composition according to the present inven ⁇ tion for treating the surface of aluminiferous metals is a waterborne surface treatment bath that forms a conversion coating on the surface of aluminiferous metals and is characterized in that it has a pH of 1.5 to 4.0 and comprises, pref ⁇ erably consists essentially of, or more preferably consists of water and the fol ⁇ lowing components: (A) at least one phosphoric acid compound,
• the aforesaid hydrogen fluoride-generating compound in the surface o treatment composition according to the present invention is preferably selected from hydrofluoric acid and ammonium fluoride.
• the aforesaid oxidizing agent in the surface treatment composition accor ⁇ ding to the present invention preferably consists of at least one selection from hydrogen peroxide, nitrous acid, organoperoxides, and salts of the preceding, s
• the aforesaid zirconium compound(s) are preferably present in a surface treatment composition according to the present invention at a total concentration of 0.005 to 0.5 g/L as zirconium.
• the aforesaid phosphoric acid compound(s) is preferably present in a sur ⁇ face treatment composition according to the present invention at a concentration 0 of 0.005 to 0.4 g/L as PO 4 "3 ions.
• the aforesaid oxidizing agent is preferably present in the surface o treatment composition according to the present invention at a concentration of 0.01 to 5.0 g/L.
• a highly sludging-inhibited process according to the present invention for treating the surface of aluminiferous metal substrates is characterized by the formation of a conversion coating on the surface of aluminiferous metal by con ⁇ tacting said surface for 0.5 to 60 seconds with a treatment bath containing any surface treatment composition as described directly above and thereafter, optionally, subjecting said surface to a water rinse and drying.
• the resulting conversion coating usually will not be uniform, because of differences in bath flow rate and surface/bath contact conditions that occur between different regions.
• the conversion coating may therefore exhibit an uneven performance.
• fluorine is consumed from the fluorocomplex of zirconium and it becomes necessary to add additional fluorine source in order to keep the zirconium stably dissolved in the bath, i.e., to keep the treatment bath transparent. This causes an even more pronounced variation in coating weight among the various regions of the can.
• the inventors discovered that the rate of the conversion coating formation reactions and the uniformity of the conversion coating can be improved through the presence of HF — in addition to zirconium, phosphoric acid, and oxidizing agent — for the purpose of stabilizing the quality by eliminating the variations in coating weight between the regions of such a shaped article that would otherwise arise from differences in reaction rate.
• Coating formation is believed to occur during treatment with a zirconium- containing treatment bath because of an increase in pH at the interface between the metal substrate and the treatment bath.
• hydrofluoric acid and aluminum fluorocomplexes present in conversion treatment baths it is known that the structures of these compounds change as a function of the pH of the treatment bath.
• Free fluoride (F), hydrofluoric acid (HF), and various aluminum fluorocomplexes may be present in an acidic aqueous solution containing aluminum and fluorine. Their proportions vary with variations in the pH of the aqueous solution. Conversion coating formation reactions are believed to occur due to the decline in the HF concentration in the vicinity of the interface. Therefore, control of the HF concentration in the treatment bath becomes necessary in order to maintain a high conversion activity and a transparent appearance on the part of the treatment bath.
• the HF concentration is measured in the present invention as follows.
• a sample of the surface treatment solution is then equilibrated at the specified temperature, and its F concentration is obtained using the calibrated fluorine ion meter and converted to the molar concentration, designated as "[F " ]".
• the pH of the treatment bath is also measured and the molar H * concentration, designated as "[H * ]”. is derived from this.
• [HF] value thus obtained is converted to g/L by multiplying by the gram molecular weight of HF.
• the following concentrations are preferred for the surface treatment composition according to the present invention: for the zirconium compound, 0.005 to 0.5 g/L as zirconium; for the phosphoric acid compound, 0.005 to 0.4 g/L as P0 4 ions; for the oxidizing agent, 0.01 to 5 g/L.
• the concentrations of the phosphoric acid compound, zir ⁇ conium compound, and oxidizing agent in the surface treatment composition ac ⁇ cording to the present invention if any of these falls below the above-specified lower limits, the resulting treatment bath will have an inadequate conversion coating formation activity and may not be able to lay down a conversion coating of sufficient thickness. No additional increases in effect are obtained when these concentrations exceed the above-specified upper limits, and such concentrations therefore serve merely to raise the cost.
• Zirconium-containing sludge is readily produced when the concentration of the hydrogen fluoride-source compound in the surface treatment composition according to the present invention falls below 0.0001 g/L as HF (hydrogen fluoride). An excessive etch, which impedes the formation of a conversion coating, occurs when this value exceeds 0.2 g/L.
• HF hydrogen fluoride
• a surface treatment process comprises the formation of a conversion coating by bringing the target surface of the aluminiferous metal substrate into contact with a treatment bath containing treat ⁇ ment composition as described above and then, optionally but preferably, exe ⁇ cuting thereon a water rinse and drying.
• Said contact between the treatment bath and metal surface may be implemented, using spray or immersion tech ⁇ nology, as a continuous one-step process or as an intermittent multi-step pro- cess.
• the total contact time preferably should be from 0.5 to 60 seconds. Because the specific component composition of the treatment bath is able to in ⁇ hibit sludge adhesion to the equipment, the described process according to the present invention can achieve an excellent operating stability and a high treat ⁇ ment efficiency.
• the surface treatment bath according to the present invention is an acidic treatment bath that contains phosphate ions, a zirconium compound, fluoride, and oxidizing agent as its essential components.
• the source of the phosphate ions in this treatment bath preferably is phosphoric acid, ammonium phosphate, and/or an alkali metal salt of phosphoric acid, with phosphoric acid and ammonium phosphate more preferred, taking into consideration sludging inhibition.
• the content is preferably 0.005 to 0.4 g/L as phosphate (P0 4 ) ions, while the range of 0.01 to 0.20 g/L as phosphate ion is even more preferred.
• a zirconium compound in treatment baths according to the present invention is most advantageously brought about through the use of water-soluble compounds of zirconium, more preferably water-soluble fluorozir- conium complexes and still more preferably fluozirconic acid (H.ZrF ⁇ ) and its salts.
• zirconium compound content is preferably 0.005 to 0.5 g/L as zirconium and is more preferably 0.01 to 0.1 g/L as zirconium. Adequate film formation may not occur at a zirconium content below 0.005 g/L. No additional benefits are obtained at concentrations in excess of 0.5 g/L, which therefore serve merely to raise the cost of the treatment bath and thus are economically undesirable.
• the presence of hydrogen fluoride in the treatment bath according to the present invention is most advantageously brought about by adding hydrofluoric acid or ammonium fluoride.
• the preferred HF content falls in the range of 0.0001 to 0.2 g/L and more preferably falls in the range of 0.01 to 0.1 g/L.
• the oxidizing agent present in the treatment bath according to the present invention is exemplified by hydrogen peroxide, nitrous acid and its salts, and or- ganoperoxides.
• the use of hydrogen peroxide is most preferred, based on a consideration of the ease of treating the waste water produced by the process according to the present invention.
• the oxidizing agent functions to accelerate the rate of the reactions that produce the zirconium coating.
• the oxidizing agent content is preferably 0.01 to 5 g/L and more preferably 0.1 to 1.0 g/L.
• the reaction-accelerating activity may be unsatisfactory at oxidizing agent concentrations below 0.01 g/L. No problems are associated with concentrations in excess of 5 g/L, but such concentrations do not provide any additional benefit, and thus merely drive up the costs and are therefore economically undesirable.
• the pH of the treatment bath should be adjusted to 1.5 to 4.0.
• the extent of etching becomes excessive at pH values below 1.5 and impedes conversion coating formation.
• the etch becomes too weak at pH values in excess of 4.0 and makes it difficult to form a highly corrosion-resistant coating.
• the preferred pH range is 2.3 to 3.0.
• the pH can be adjusted through the use of an acid such as phosphoric acid, nitric acid, or hydrochloric acid, or through the use of an alkali such as ammonium hydroxide, ammonium carbonate, or sodium hydroxide.
• Phosphoric acid and nitric acid are the preferred acids for adjusting the pH, while basic ammonium compounds are preferred as the alkali.
• the stability of the treatment bath can be substantially impaired by metal ions, such as those of copper, manganese, and the like, that are produced when an alloying component is eluted from the surface of the aluminiferous metal substrate. This can result in such problems as sludge production, precipitate formation, and the adhesion of sludge and/or precipitate to the equipment and the like.
• an organic acid or salt thereof for example, gluconic acid, oxalic acid, and their salts, may be added in order to chelate such components and stabilize the bath.
• a water-soluble fluorocomplex of, for example, titanium, silicon, and the like, may also be added to the surface treatment bath according to the present invention along with the zirconium compound, for example, a water-soluble fluorozirconium complex.
• An example of the surface treatment process according to the present invention for an aluminiferous metal substrate includes the following steps: (1) surface cleaning: degreasing (acidic, alkaline, or solvent-based degreasers may be used)
• the treatment temperature with the surface treatment bath according to the present invention is not crucial, and, for example, a temperature range from room temperature to 90 °C can be used. However, taking into consideration the stability, operating behavior, and productivity characteristics of the treatment bath, the bath is preferably used at from 25 °C to 50 °C.
• the treatment time is also not crucial, but treatment times of, for example, 0.5 to 60 seconds are preferred and the range of 5 to 30 seconds is even more preferred. A full reaction is not usually obtained in less than 5 seconds; this would prevent the formation of a highly corrosion-resistant coating. At the other end of the range, no additional increase in performance has been observed at times above 60 seconds.
• the materials were aluminum alloy (A3004) sheets and aluminum Dl cans fabricated from this type of aluminum alloy sheet. These were each cleaned, prior to surface treatment according to this invention, with a hot aqueous solution of an acidic degreaser (PALKLINTM 500, a product of Nihon Parkerizing Company, Limited, Tokyo). 12) Evaluation methods (a. Corrosion resistance and coating uniformity The corrosion resistance and coating uniformity were evaluated on the aluminum Dl cans based on the resistance to blackening by boiling water. The resistance to blackening by boiling water was tested as follows. After surface treatment, the aluminum Dl cans were immersed in boiling tap water for 30 min ⁇ utes.
• the treatment bath which had been used in the particular example or comparative example was held at 40 °C for 15 days.
• the amount of zirconium in the bath was measured both before and after this holding period, and the presence/absence of precipitate was determined from the difference in these values. A “+” indicates that precipitate was not produced, while “x” indicates that precipitate was produced.
• the cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 20 seconds with surface treatment bath (1) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• the aluminum nitrate was used as an aluminum source for the purpose of artificially aging the treatment bath.
• Example 2 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 40 seconds with surface treatment bath (2) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rins ⁇ ing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• the cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 15 seconds with surface treatment bath (3) (composition given below) heated to 40 ⁇ C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• the cleaned aluminum Dl cans and cleaned aluminum alloy sheets were immersed for 10 seconds in surface treatment bath (4) (composition given below) heated to 30 °C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Example 5 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 5 seconds with surface treatment bath (5) (composition given below) heated to 30 °C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Surface treatment bath (5.
• Example 6 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 15 seconds with surface treatment bath (6) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rins ⁇ ing for 10 seconds with deionized water, and then drying in a hot-air drying oven.
• surface treatment bath (6) composition given below
• Example 7 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 15 seconds with surface treatment bath (7) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rins ⁇ ing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 1 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 10 seconds with surface treatment bath (8) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 2 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 10 seconds with surface treatment bath (9) (composition given below) heated to 50 °C. This was followed by rinsing with tap water, spray rins ⁇ ing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 3 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 20 seconds with surface treatment bath (10) (composition given below) heated to 35 °C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 4 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 15 seconds with surface treatment bath (11) (composition given below) heated to 40 ⁇ C. This was followed by rinsing with tap water, spray rinsing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 5 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 10 seconds with surface treatment bath (12) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rins- ing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Comparative Example 7 The cleaned aluminum Dl cans and cleaned aluminum alloy sheets were sprayed for 30 seconds with surface treatment bath (14) (composition given below) heated to 40 °C. This was followed by rinsing with tap water, spray rins- ing for 10 seconds with deionized water, and then drying in a hot-air drying oven. The samples thus obtained were evaluated for their corrosion resistance, coating uniformity, and paint adherence.
• Examples 1 to 7 used surface treatment baths and surface treatment pro-vics according to the present invention, and Table 1 confirms the following results for these examples: the obtained conversion coatings exhibited an excellent corrosion resistance and paint adherence; the obtained conversion coatings were very uniform; the surface treatment baths maintained their trans ⁇ parency; and sludge adhesion was thoroughly inhibited.
• Com- parative Examples 1 to 7 which used surface treatment baths outside the scope of the invention — in each case gave an unsatisfactory overall perform ⁇ ance because each was found to be deficient in at least one aspect (corrosion resistance, paint adherence, conversion coating uniformity, treatment bath transparency, and inhibition of sludge adhesion).
• the surface treatment composition and surface treatment process accord ⁇ ing to the present invention impart an excellent corrosion resistance and ex ⁇ cellent paint adherence to the surface of aluminiferous metal substrates prior to the painting thereof.
• Other desirable effects demonstrated by this composition and process are a very uniform conversion coating, excellent treatment bath transparency, and an excellent inhibition of sludge adhesion.

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• Chemical Treatment Of Metals (AREA)

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• 1994
  • 1994-12-22 JP JP32054594A patent/JP3349851B2/ja not_active Ceased
• 1995
  • 1995-12-13 ZA ZA9510615A patent/ZA9510615B/xx unknown
  • 1995-12-15 AR AR33464295A patent/AR000514A1/es unknown
  • 1995-12-22 BR BR9510243A patent/BR9510243A/pt not_active Application Discontinuation
  • 1995-12-22 CA CA 2208459 patent/CA2208459A1/en not_active Abandoned
  • 1995-12-22 AU AU44697/96A patent/AU4469796A/en not_active Abandoned
  • 1995-12-22 WO PCT/US1995/016231 patent/WO1996019595A1/en not_active Application Discontinuation
  • 1995-12-22 EP EP95943426A patent/EP0799326A4/en not_active Withdrawn
  • 1995-12-22 TR TR95/01662A patent/TR199501662A2/xx unknown

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