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
  • C23C22/37—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 hexavalent chromium compounds
  • C23C22/38—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 hexavalent chromium compounds containing also phosphates

Definitions

• the present invention relates to a novel conversion treatment solution for aluminum and aluminum alloys which imparts an excellent corrosion resistance and paint adher- ence to the surface of aluminum and aluminum alloys prior to their being painted and to a process of treating sur ⁇ faces with such a solution.
• the conversion treatment solu ⁇ tion is particularly well suited for application to the surface of, for example, the lid material for beverage cans (i.e., can end stock) and the like.
• Conversion treatment solutions for aluminum and alum ⁇ inum alloys may be roughly classified into chromate-type treatments and nonchromate-type treatments.
• Typical exam- pies of chromate-type treatments are chromic acid/chromate treatments and phosphoric acid/chromate treatments.
• Chrom ⁇ ic acid/chromate treatments came into practical application in about 1950, and are still widely used at present on, for example, the fin material of heat exchangers.
• the princi- pal components of this type of conversion treatment solu ⁇ tion are chromic acid (Cr0 3 ) and hydrofluoric acid (HF) , and an accelerator may also be present.
• a film which con ⁇ tains some quantity of hexavalent chromium is formed.
• the phosphoric acid/chromate conversion treatment is disclosed in United States Patent Number 2,438,877.
• This conversion treatment solution is composed of chromic acid
• Nonchromate-type treatments are recognized in the art as a distinct category from the chromate-type treatment so- lutions explained above, and are exemplified by the inven- tion disclosed in Japanese Patent Application Laid Open [Kokai] Number 52-131937 [131,937/77].
• the treatment solu ⁇ tion disclosed therein comprises an acidic (pH approximate ⁇ ly 1.0 to 4.0) aqueous coating solution which contains zir- conium or titanium or a mixture thereof as well as phos ⁇ phate and fluoride.
• Treatment with the disclosed conver ⁇ sion treatment solution produces on the aluminum surface a conversion film whose main component is zirconium and/or titanium oxide.
• this type of treatment solution nevertheless suffers from a corrosion resistance and paint adherence inferior to those for chromate-type treatments.
• Aluminum alloy, in sheet or coil form, is widely used after painting for beverage can lid material, i.e., can end stock. It is subjected to a conversion treatment in order to raise the corrosion resistance and paint adherence, and the phosphoric acid/chromate treatment is employed in al ⁇ most all commercial can lid manufacturing in Japan.
• the phosphoric acid/chromate conversion treatment of can end stock generally employs a treatment solution which contains 10.0 to 40.0 g/L phosphate ion, 2.0 to 4.0 g/L hexavalent chromium, and 0.7 to 1.5 g/L fluoride ion.
• vinyl chloride paint is generally used to coat can end stock.
• the production of can ends normally in ⁇ cludes a phosphoric acid/chromate treatment of aluminum alloy in coil or sheet form, followed by coating with a vinyl chloride paint and then forming.
• a beverage can thus normally consists of a can end formed from aluminum alloy coil or sheft treated as de ⁇ scribed above and of a can body filled with, for example, juice or beer.
• the can may be subjected to sterilization at relatively high temperatures after filling. If it is, steam is formed from vaporiza- tion of the contents, the steam penetrates through the paint film, and the permeated steam then condenses at the interface between the paint film and conversion film. As a result, sterilization tends to reduce the adherence of the paint film.
• defects enamel feathering
• the present invention in ⁇ troduces an aqueous conversion treatment solution for alum ⁇ inum and aluminum alloys which is characterized in that its pH is in the range from 1.0 to 3.0 and in that it compris ⁇ es, or preferably consists essentially of, water and 5.0 to 40.0 grams per liter ("g/L") of phosphate ions, 1.0 to 4.0 g/L of hexavalent chromium (in the form of chromium con ⁇ taining anions) , 0.1 to 2.0 g/L of fluoride ions, and a complex fluoride ion component selected from the group consisting of (i) 4.0 to 15.0 g/L of fluosilicate ion, (ii) 0.5 to 3.0 g/L of fluoborate ion, (iii) 2.0 to 8.0 g/L of fluozirconate ions, and (iv) 2.0 to 8.0
• This conversion treatment solution is capable of forming a highly paint-adherent conversion film which im ⁇ parts an excellent corrosion resistance to the surface of aluminum and aluminum alloys.
• the present invention seeks to offer a conversion treatment solution which imparts an excellent corrosion resistance and paint adherence to the surface of aluminum and aluminum alloy prior to their being painted. Details of Preferred Embodiments of the Invention
• the conversion treatment solution of the present invention is an acidic treatment solution which contains complex fluoride ion, phosphate ion, hexavalent chromium, and fluoride ion as its essential components.
• the complex fluoride ions are selected from fluosili- cate (SiF, —2) ions, fluotitanate (TiF g —2), fluozirconate
• —2 —2 ZrF 6 ' ' and fl uo * DOrate ( BF 4 ) ions may be added in the form of fluosilicic acid, fluoboric acid, fluozirconic acid, fluotitanic acid, or any soluble salt thereof. Mix ⁇ tures of these ions may also be used.
• a range of 4.0 to 15.0 g/L is preferred for the fluosilicate ion. Values less than 4.0 g/L cannot normally generate good paint ad ⁇ herence, while values exceeding 15.0 g/L may cause substan ⁇ tial etching of an aluminum surface and prevent the forma ⁇ tion of a satisfactory film.
• a range of 0.5 to 3.0 g/L is preferred for the fluoborate ion. Values less than 0.5 g/L again cannot usually generate a good paint adherence, while values in excess of 3.0 g/L increase waste water pollution and are uneconomical.
• a range of 2.0 to 8.0 g/L is pre ⁇ ferred for fluozirconate ions, fluotitanate ions, or mix ⁇ tures of these two ions. Concentrations of these two com- plex fluoride ions that are less than 2.0 g/L cannot usu ⁇ ally generate good paint adherence, while concentrations exceeding 8.0 g/L cause substantial etching and usually prevent the formation of a satisfactory film.
• Phosphoric acid (H_PO.) is the preferred source for the phosphate ion, and the preferred phosphoric acid con ⁇ tent falls into the range of 5.0 to 40.0 g/L. When this value is less than 5.0 g/L, the resulting film will nor ⁇ mally contain only small quantities of chromium phosphate and the paint adherence may be inadequate. While good films are formed at concentrations exceeding 40.0 g/L, the cost of the treatment solution is also increased and the economics become less favorable.
• Chromic acid is the preferred source for the hexavalent chromium, and the preferred chromic acid content is that which will result in a concentration of its stoi- chio etric equivalent as hexavalent chromium in the range from 1.0 to 4.0 g/L. Values less than 1 g/L result in an inferior corrosion resistance because a satisfactory con ⁇ version film is not formed. Values in excess of 4.0 g/L can cause increased pollution from and/or pollution abate ⁇ ment cost for waste water from the treatment solution and thus create environmental and economic problems.
• the fluoride ion content is an important component for controlling the film growth rate of the conversion film.
• the fluoride ion source may be, for example, hydrofluoric acid (HF) , sodium fluoride (NaF) , potassium fluoride (KF) , and the like.
• the fluoride ion concentration in the con ⁇ version solutions was determined as follows: An ion-selec ⁇ tive electrode (Fluorine F-125 electrode, reference HS- 305DP from Toa Denpa Kogyo Kabushiki Kaisha) and an ion meter (Type IM-40S from Toa Denpa Kogyo Kabushiki Kaisha) were used.
• the pH of the conversion solution itself was adjusted to 2.0 using phosphoric acid or sodium hydrox ⁇ ide and then measured using the fluorine ion meter, and the measured value was converted to the fluoride ion concentra ⁇ tion by reference to the calibration curve.
• the preferred range for the fluoride ion concentration is 0.1 to 2.0 g/L. At values less than 0.1 g/L, the growth rate of the conversion film is slow, so that long treatment times must be used in order to obtain satisfactory conver ⁇ sion films and the productivity is therefore low. Rapid growth rates are encountered at values in excess of 2.0 g/L; this results in large film weights and an undesirable loss of the metallic luster of the workpiece.
• the preferred concentration range is 0.1 to 2.0 g/L; the particularly preferred range is 0.4 to 1.0 g/L.
• the pH of this conversion treatment solution should be in the range of 1.0 to 3.0 and may conveniently be adjusted into that range through the use of an acid arbitrarily se ⁇ lected from acids such as phosphoric acid, nitric acid, and hydrochloric acid or a base arbitrarily selected from bases such as sodium hydroxide, ammonium hydroxide, and the like.
• a pH below 1.0 causes substantial etching and therefore in- terferes with coat formation.
• a pH in excess of 3.0 usu ⁇ ally results in weak etching so that a uniform film cannot be formed.
• the conversion treatment solution of the present invention can be used as a substitute for the currently widely used phosphoric acid/chromate treatment solutions.
• a preliminary surface cleaning must usually be carried out when the conversion treatment solution of the present in ⁇ vention is used for the conversion treatment of the surface of aluminum or aluminum alloy.
• the cleaning method in this case may consist of treatment with an acidic, alkaline, or solvent-based cleaning solution or some combination there- of.
• the aluminum or aluminum al ⁇ loy surface may be etched with alkali or acid after clean ⁇ ing. Either immersion or spray treatment may be used as the method for treatment with solution according to the present invention.
• the weight of the resulting conversion film is governed by such factors as the treatment tempera ⁇ ture and treatment time.
• the temperature of the treatment solution should preferably fall into the range from room temperature (about 20 degrees Centigrade) to 70 degrees Centigrade and more preferably falls into the range from 35 to 55 degrees Centigrade. Treatment times in the range of 1 to 90 seconds are preferred.
• the conversion film weight is normally evaluated based on the deposition of chromium, zirconium, and/or titanium. The quantity of deposition of each of the three metals, when present at all, preferably falls within
• chromium, titanium, and/or zirconium can be controlled by suitably adjusting the treatment tempera ⁇ ture and treatment time.
• the conversion film formed by the conversion treatment solution according to the present invention when neither zirconium or titanium is present is believed to be chemi ⁇ cally and physically similar to the film formed by phos ⁇ phoric acid/chromate treatments, and is composed princi ⁇ pally of hydrated chromium phosphate (CrP0 4 »4H 2 0) .
• the conversion film usually contains both hydrated chromium phosphate and zirconium oxide (ZrO_) and/or titanium oxide (TiO_) .
• the conversion treatment solution of the present in ⁇ vention is explained in greater detail below through the use of several illustrative examples.
• the first group of examples are for solutions containing fluoborate or fluo- silicate ions, and the effectiveness of such solutions rel ⁇ ative to comparison examples is reported in Table 1.
• the substrate for these examples was an aluminum/mag ⁇ nesium alloy (described in detail in Japanese Industrial Standard ⁇ hereinafter "JIS") A5082) .
• JIS Japanese Industrial Standard
• This aluminum alloy was degreased and conversion treated using a small sprayer designed to give spraying conditions identical to those currently encountered in typical spray treatments on com ⁇ flashal continuous conversion treatment lines for the con ⁇ version treatment of aluminum alloy coil.
• Chromium content in the coating deposited by the conversion process was mea ⁇ sured using a fluorescent X-ray analyzer (Model 3070E from
• Salt-spray testing was conducted in order to evaluate the corrosion resistance. Salt-spray testing was conducted in accordance with JIS Z-2371, and the value reported is the time required for the appearance of blistering at a cross form cut in the paint film on the painted test panel. Thus, longer times correspond to a better corrosion resist- ance. Spray times of 2000 hours or more are generally now rated as excellent.
• the paint adherence was evaluated as follows The painted test sheet was cut into 5 x 150 millimeter (herein- after "mm") size rectangular strips, which were then hot- press-bonded with polyamide film. The obtained test spec ⁇ imen was immersed in boiling deionized water for 3 hours, and the peel strength was then evaluated in a 180° peel test. High peel strength values correspond to a better paint adherence, and as a general rule a value of 3.0 kilo ⁇ grams of force (hereinafter "kgf") per 5 mm width is rated as excellent.
• kgf 3.0 kilo ⁇ grams of force
• Enamel feathering was evaluated in accordance with the Alcoa method, as described on page 49 of the Lecture Notes from the 73rd Fall Meeting of Keikinzoku Gakkai [Institute of Light Metals of Japan] . This evaluation is based on the maximum residual paint film width after peeling. Thus, smaller residual paint film widths correspond to a more de ⁇ sirable smaller amount of enamel feathering, and as a gen- eral rule residual widths not exceeding 0.5 mm are rated as excellent.
• the surface of the aluminum alloy was cleaned by rins ⁇ ing with a hot (70 degrees Centigrade) 4 % aqueous solution of a commercial strongly alkaline degreaser (FINE CLEANERTM 4418 from Nihon Parkerizing Company, Limited) and then with water. This was followed by spraying for 5 seconds with conversion treatment solution 1 heated to 50 degrees Cent ⁇ igrade, rinsing again with tap water, spraying with deion- ized water (specific resistance > 3,000,000 ohm-cm) for 10 seconds, and finally drying in a hot-air drying oven at 70 degrees Centigrade for 5 minutes. After drying, the con ⁇ version coated test panel was painted as described above, and the corrosion resistance, paint adherence, and enamel feathering were then evaluated.
• FINE CLEANERTM 4418 commercial strongly alkaline degreaser
• Example 2 Example 2
• Example 7 Example 7
• Example 8 This was identical to Example 1, except that the sam ⁇ ples were spray treated for 10 seconds at 40 degrees Centi- grade rather than for 5 seconds at 50 degrees Centigrade as in Example 1.
• Example 8 This was identical to Example 1, except that the sam ⁇ ples were spray treated for 10 seconds at 40 degrees Centi- grade rather than for 5 seconds at 50 degrees Centigrade as in Example 1.
• Example 1 This was identical to Example 1, except that the sam- pies were spray treated for 10 seconds rather than for 5 seconds as in Example 1. Comparison Example 1
• Example 4 The aluminum alloy was cleaned as in Example 1 and then spray-treated for 5 seconds with a 5 % aqueous solu- tion of a commercial phosphoric acid/chromate treatment concentrate (ALCHROMTM K702 from Nihon Parkerizing Company, Limited) heated to 50 degrees Centigrade. After this treatment, it was rinsed with water, dried, and painted as in Example 1, and its performance was then evaluated. Comparison Example 4
• Example 2 The aluminum alloy was cleaned as in Example 1 and then spray-treated for 30 seconds with a 2 % aqueous solu ⁇ tion of a commercial non-chromate treatment concentrate (PARCOATTM K3761 from Nihon Parkerizing Company, Limited) heated to 50 degrees Centigrade. After this treatment, it was rinsed with water, dried, and painted as in Example 1, and its performance was then evaluated.
• PARCOATTM K3761 commercial non-chromate treatment concentrate
• Example 10
• Example 13
• _.__ fluotitanic acid 4.0 g/L of TiF g instead of the fluo- zirconic acid in Conversion Solution 9 in Example 9 and (ii) had a pH of 2.5 achieved by adjustment with sodium hy ⁇ droxide rather than a pH of 2.0 achieved by adjustment with ammonia as in Conversion Solution 9.
• Example 15 This was identical to Example 9, except that the sam ⁇ ples were spray treated for 10 seconds at 40 degrees Centi ⁇ grade rather than for 5 seconds at 50 degrees Centigrade as in Example 9.
• Example 16 This was identical to Example 9, except that the sam ⁇ ples were spray treated for 10 seconds rather than for 5 seconds as in Example 9. Comparison Example 5

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• 1991
  • 1991-02-13 CA CA 2072592 patent/CA2072592A1/en not_active Abandoned
  • 1991-02-13 BR BR919106049A patent/BR9106049A/pt unknown
  • 1991-02-13 AU AU73370/91A patent/AU642478B2/en not_active Ceased
  • 1991-02-13 WO PCT/US1991/000965 patent/WO1991013186A1/en active IP Right Grant
  • 1991-02-13 EP EP91904950A patent/EP0516700B1/de not_active Expired - Lifetime
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