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
• • 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
  • C23C22/78—Pretreatment of the material to be coated

Definitions

• a preferred chromate conversion coating solution for use in this method is one which contains at least 0.5 gram per liter of zinc ions, from about 0.5 to 4.5 grams per liter of hexavalent chromium ions, calculated as CrO from about 0.5 to grams per liter of sulfate ions and at least 0.15 gram per liter of a fluoride radical.
• the solution may also contain at least 0.25 gram per liter of trivalent chromium ions.
• This invention relates to improved compositions and processes for providing a protective coating on metal surfaces and more particularly it relates to such improved compositions and processes for providing surfaces which are predominately of zinc or aluminum with a protective chromium-containing coating of the chemical conversion type.
• zinciferous surfaces it is intended to refer to alloys wherein zinc is the principal ingredient, as well as to hot-dipped galvanized surfaces, electro-deposited zinc coatings and to essentially pure zinc surfaces.
• the chromate conversion coatings for such zinciferous surfaces must provide protection for the surface coated against corrosion and also must have good paint bonding qualities, so as to serve as a paint base material.
• an object of the present invention to provide an improved coating material of the chromate conversion type, which coating material may be applied to aluminum or zinciferous surfaces even on high speed strip lines.
• Another object of the present invention is to provide an improved chromate conversion coating for application to aluminum or zinciferous surfaces, which coating has consistently good corrosion resistance and paint bonding qualities.
• a further object of the present invention is to provide an improved process for treating surfaces which are predominantly of Zinc or aluminum so as to provide thereon a chromate conversion coating having good corrosion resistance and paint bonding qualities.
• the present invention includes a process for treating surfaces which are predominantly of zinc or aluminum, which process comprises contacting the surface to be treated with an alkaline solution having a pH of at least about 11, maintaining the alkaline solution in contact with the surface for a period of time sufiicient to activate the surface, contacting the thus-activated surface with a chromate conversion coating solution, maintaining said coating solution in contact with the metal surface for a period of time sufficient to effect formation of the desired chromate conversion coating thereon and, thereafter, contacting the thus-coated surface with an aqueous solution containing hexavalent chromium, calculated as CrO in an amount of at least 0.025 percent by weight of the solution.
• a zinciferous surface is activated by contacting it with an alkaline solution having a pH within the range of about 12 to about 13.5, and preferably having an alkali concentration within the range of about 3 to about 12 grams per liter.
• alkaline solutions which will provide the desired pH as has been indicated hereinabove, may be used.
• these solutions are aqueous solutions containing alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, alkali metal silicates, and the like.
• alkali metal phosphates which may be included in the composition are the trialkali metal phosphates, the tetra-alkali metal pyrophosphates, the alkali metal tripolyphosphates, and the like.
• alkali metal compound is intended to refer to the compounds of lithium, sodium, potassium, cesium, and rubidium.
• the preferred alkali metal compounds are generally those of sodium and, accordingly, specific reference will be made hereinafter to such compounds. This is not, however, to be taken as a limitation of the alkali metal compounds which may be used as other alkali metal compounds, and particularly potassium compounds have been found to be suitable for use in the process of the present invention.
• the preferred compounds for formulating the treating composition are the alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, trisodium or tripotassium phosphate, and the alkali metal orthosilicates, such as sodium orthosilicate.
• the aqueous alkaline solution may be applied to the zinciferous surface to be treated using various techniques, such as immersion, flooding, spraying and the like, with spraying techniques generally being preferred.
• the alkaline solution at the time of application to the zinciferous surface is at an elevated temperature, with temperatures within the range of about 60 to about 90 degrees centigrade being typical and temperatures within the range of 65 to about 80 degrees centigrade being preferred.
• the hot alkaline solution is maintained in contact with the surface to be treated for a period of time sufficient to effect the desired activation of the zinciferous surface. Generally, contact times of up to about 2 minutes are typical, with contact times of about seconds to about 1 minute being preferred.
• the zinciferous surface After the zinciferous surface has been treated with the alkaline solution, it is brought into contact with a chromate conversion coating material for a period of time suflicient to effect the formation of the desired chromate conversion coating on the zinc surface.
• a chromate conversion coating material used may be of various types, including one of the numerous conventional chromate conversion coating materials which are known in the art.
• the zinc surface is subjected to a water rinse both before and after the application of the chromate conversion coating material.
• any alkaline solution remaining on the zinc surface is removed before the surface is contacted with the chromate conversion coating material, and, similarly, any non-reacted conversion coating material is removed from the surface prior to subsequent treating steps.
• the rinsing operation may be carried out in any convenient manner, as for example, by immersing, spraying, or flooding the treated surface with water.
• the thus-coated surface is then contacted with an aqueous solution containing hexavalent chromium, calculated as CrO in an amount within the range of about 0.025 to about 0.35 percent by weight of the aqueous solution.
• This solution may be applied to the surface to be treated using various means, including roller, immersion, flooding, or spraying techniques, and the like, with spraying techniques being preferred. Additionally, if desired, after the application of the hexavalent chromium solution to the surface the excess of this solution may be removed from the surface, preferably by wiping or squeegeeing.
• the concentration of the hexavalent chromium solution is desirably within the range of about 0.06 to about 0.35 percent by weight of the solution and preferably within the range of about 0.07 to about 0.15 percent by weight of the solution.
• the concentration of the hexavalent chromium, calculated as CrO is desirably within the range of about 0.025 to about 0.2 percent by weight of the solution and preferably within the range of about 0.05 to about 0.1 percent by weight of the solution.
• the aqueous hexavalent chromium solution used is a water solution containing a source of hexavalent chromium, in the amounts as have been indicated hereinabove.
• Various water-soluble or water dispcrsible sources of hexavalent chromium may be used in formulating this solution, provided the anions or cations introduced with the hexavalent chromium do not have a detrimental effect on either the solution itself or on the coated zinc surfaces which are treated.
• hexavalent chromium materials which may be used are chromic acid (CrO the alkali metal chromates, such as sodium chromate and potassium chromate, the alkali metal dichromates, such as sodium dichromate and potassium dichromate, and the like.
• the aqueous hexavalent chromium containing solution is maintained at an elevated temperature while it is in contact with the surface to be treated, temperatures within the range of about 35 to about 60 degrees centigrade and contact times of up to about 60 seconds being typical.
• chromate conversion coating materials may be used with the process of the present invention.
• Exemplary, but by no means all inclusive of the chromate conversion coating composition which may be used are those described in U.S. Patents 2,035,380, 2,296,884, 2,393,640, 2,393,633, 2,393,664, 2,393,665, 2,477,310, 2,483,510, 2,494,908, 2,497,905, 2,499,231, 2,504,434, 2,524,577, 2,796,372, 2,799,601, 2,843,513, 2,844,496 3,090,710, 3,130,085 and 3,130,086.
• the chromate conversion coating composition used in the process of the present invention is an aqueous solution which comprises at least 0.5 gram per liter of zinc ions, from 0.5 to about 4.5 grams per liter of hexavalent chromium ions, calculated as CrO from about 0.5 to about 40 grams per liter of sulfate ions and at least 0.15 gram per liter of a fluoride radical.
• This composition when applied to surfaces which are predominantly of zinc or aluminum, produces a chromate conversion coating which is highly corrosion resistant and has excellent paint bonding characteristics. Accordingly, this composition is the preferred chromate conversion coating material for use in the process of the present invention.
• the zinc ions which are calculated as Zn, are present in an amount of at least 0.5 gram per liter and preferably in an amount within the range of about 1 to about 15 grams per liter.
• the zinc ions may be added to the composition of the present invention in any convenient form which is water dispersible and preferably water soluble, provided that when the zinc is added as a zinc salt, the anion portion of the salt does not have a detrimental effect on either the solution itself or on the coating which is ultimately produced.
• the Zinc may be added to the present composition as zinc oxide, zinc sulfate, zinc dichromate, zinc fluosilicate, and the like, or, in some instances, may even be added as zinc metal.
• the zinc is added to the composition as the salt of one of the other anions which are part of the composition, and preferably as the zinc sulfate.
• the hexavalent chromium ion this is calculated as CrO and is present in the composition in an amount within the range of about 0.5 to about 4.5 grams per liter, and preferably in an amount within the range of about 1 to about 3 grams per liter.
• the hexavalent chromium ions may be introduced into the present composition in any suitable water dispersible form in which the anions or cations introduced with the hexavalent chromium are not detrimental to the composition or the subsequently produced coating.
• the hexavalent chromium ions may be added to the composition in the form of chromic acid, CrO or, as it is sometimes referred to, chromic trioxide.
• the hexavalent chromium may be introduced into the composition as a hexavalent chromium salt of zinc, such as zinc chromate or zinc dichromate.
• the sulfate ions in the present composition are present in an amount within the range of about 0.5 to about 40 grams per liter and preferably in an amount within the range of about 2 to about 35 grams per liter.
• the sulfate ions may be added as sulfuric acid.
• the preferred aqueous acidic composition for use in the process of the present invention also contains a fluoride radical in an amount of at least 0.15 gram per liter, and preferably in an amount within the range of about 1 to about grams per liter.
• Typical of the fluoride radicals which may be utilized in the present composition are complex fluoride radicals such as fluotitanate (TiF fluoborate (BF fluosilicate (SiF and fluoaluminate (AlF as well as simple fluoride radical, i.e., (F)-.
• These may be introduced into the composition in any substantially water dispersible and preferably water soluble form, such as in the form of the corresponding zinc salt.
• a complex fluoride radical such as the fluosilicate radical, it may be introduced into the composition as the acid, i.e., fluosilicic acid or as HF.
• trivalent chromium ions generally in an amount of at least about 0.25 gram per liter, and preferably in an amount within the range of about 3 to about 9 grams per liter.
• the trivalent chromium is desirably introduced into the composition as chromic sulfate although other trivalent chromium salts may also be used, provided that the anions of these salts have no detrimental effect on either the coating solution or on the coatings produced on the surfaces treated.
• nitrate ions in addition to the trivalent chromium ions, in many instances, it has also been found to be desirable to incorporate in the composition of the present invention nitrate ions in an amount of at least 0.05 percent by weight of the composition. Generally, it is preferred that where nitrate ions are included in the composition, they are added as nitric acid although water dispersible nitrate salts may also be used. Where the nitrate ions are added in the preferred manner, i.e., as nitric acid, it is generally desirable that the amount of nitric acid added is not sufficient to lower the pH of the solution below that at which the efficient coating of the zinc or aluminum surfaces is obtained.
• the pH of the coating solution of the present invention be maintained within the range of about 0.62 to about 3.5 with a pH value within the range of about 1.6 and about 2.5 being preferred. Accordingly, with regard to the addition of nitric acid to the present composition, it is desirable that the quantity of the nitric acid added is not sufficient to lower the pH of the solution below about 0.62. It will be appreciated by those in the art, that the desired pH of the present coating solution may be maintained by adjusting the amounts of the various components of the composition, within the ranges as has been indicated hereinabove. Generally, and perhaps most typically, the pH of the solution will be adjusted by the addition of sulfuric acid thereto.
• the subject coating composition will be in aqueous acid solution having a pH within the range of about 1.6 to about 2.5, which contains the following components in amounts indicated: Zinc, calculated as Zn, from about 1 to 15 grams per liter, hexavalent chromium, calculated as CrO from about 1 to about 3 grams per liter, sulfate ions, calculated as 80, from about 2 to about 35 grams per liter, complex fluorides, such as SiF in an amount of at least about 0.15 gram per liter. Desirably, the composition will also contain trivalent chromium in an amount of at least about 0.25 gram per liter.
• the chromate conversion coating solution may be applied to the zinciferous surfaces to be treated using various coating techniques.
• the coating may be applied by immersing the surfaces to be coated in the coating solution, or by applying the solution to the surfaces by means of coating rolls, flooding, spraying, and the like.
• spraying techniques are preferred for applying the chromium conversion coating compositions.
• the temperatures at which the chromate conversion coating compositions are applied have not been found to be critical, the temperature of the compositions being variable over a relatively wide range.
• application temperatures within the range of about room temperature, i.e. about 20 degrees centigrade, up to 70 degrees centigrade are typical with temperatures within the range of about 25 to about 45 degrees centigrade being preferred.
• temperatures within the range of about 25 to about 45 degrees centigrade.
• even lower temperatures such as temperatures as low as 12 degrees centigrade as Well as higher temperatures, such as to degrees centigrade have also been used to obtain excellent chromate conversion coatings on the surfaces treated.
• the zinc surfaces to be coated are treated with an alkaline solution, as has been heretofore described, which solution is preferably at a temperature of about 65 to 80 degrees centigrade and may be applied to the surface being treated using the various application techniques as indicated hereinabove, with the spraying techniques being preferable.
• the surface is desirably rinsed in water, and preferably in a hot water spray using water at a temperature within the range of about 60-85 degrees centigrade.
• a chromate conversion coating solution and preferably the preferred composition described above is applied to the zinc surface, desirably by spraying.
• the thus formed coating is preferably given a cold water rinse, again preferably using a Water spray, and is then contacted with the above described aqueous hexavalent chromium rinse solution, preferably by spraying the hexavalent chromium solution at a temperature within the range of about 35 to about 55 degrees centigrade.
• the excess moisture is preferably removed from the treated zinc surface, as by means of a squeegee, and the surface is then dried, temperatures within the range of about 100 to degrees centigrade and times up to about 5 minutes being typical.
• the temperatures are expressed in degrees centigrade and the parts and percentages are by weight.
• the coating compositions are applied to high-speed continuous ht-dip galvanized surfaces, known commercially as zincgrip and said to be obtained by the continous hot-dip zinc coating process disclosed in US. Patent 2,197,622. After these surfaces were coated, they were painted with a vinyl paint and then subjected to a percent salt spray, humidity and physical tests.
• the salt spray test is the American Society for Testing and Materials (ASTM) test B117-61 with painted panels scribed as given in ASTM test D-1654-61. This uses a 5 percent sodium chloride fog. The ratings given depend on the creepage from the scratch, given in of an inch.
• Example pH CrO Cr Zn+ SO F- N03 Alkaline treating solutions were also formulated by admixing in Water, in the amounts indicated, the components as set forth in the following table:
• the thus-rinsed panels were squeegeed and then oven dried for about 1 minute at 120 degrees Centigrade.
• the thus-dried panels were then painted with the vinyl paint, cured for 10 minutes at about 150 degrees centigrade and then subjected to the 5 percent salt spray test as described above.
• the panels were found to exhibit only trac amounts of corrosion, substantially all the panels having ratings within the range of 0-2.
• the panels were also subjected to the humidity, adhesion and physical tests, as described above. In all instances, after the humidity test, the panels tested had ratings of F and VF.
• the ratings after the adhesion test on substantially all panels was 810, with most of the panels having a rating of 10. In the physical testing, substantially no peeling was encountered and in all cases, the ratings were less than about 8 percent.
• a process for treating surfaces which are predominantly of zinc or aluminum which process comprises contacting the surface to be treated with an alkaline solution having a pH of at least about 11, maintaining the alkaline solution in contact with the surface for a Components in grams/liter Alkaline solution N 2.0 H Trisodium N220 O 3 Wetting agent Sequentering Sodium ortho Sodium Petroleum pH phosphate agent sihcate tnpolydlstillate phosphate The zincgrip panels were sprayed with one of the above alkaline solutions for 30 seconds, the solution being period of time suificient to activate the surface, which contact time is at least 15 seconds, contacting the thusat a.
• chromate conversion coating solution having a pH within the range of about 0.62 to 3.5
• said chromate conversion coating solution comprising zinc ions in an amount of at least 0.5 gram per liter, hexavalent chromium ions, calculated as CrO in an amount within the range of about 0.5 to 4.5 grams per liter, sulfate ions in an amount within the range of about 0.5 to about 40 grams per liter, and at least 0.15 gram per liter of a fluoride radical, maintaining said coating solution in contact with said surface for a period of time sufficient to effect formation of the desired chromate conversion coating thereon and, thereafter, contacting the thus-coated surface with an aqueous solution containing hexavalent chromium, calculated as CrO in an amount of at least 0.25% by weight of the solution.
• the chromate conversion coating solution is comprised of zinc ions in an amount within the range of about 1 to about grams per liter, hexavalent chromium ions, calculated as CrO in an amount within the range of about 1 to about 3 grams per liter, sulfate ions in an amount within the range of about 2 to about 35 grams per liter, from about 1 to about 15 grams per liter of a complex fluoride radical selected from the group consisting of fluotitanites, fluoborates, fluosilicates, fluoaluminates, and from about 3 to about 9 grams per liter of trivalent chromium ions.
• a chromate conversion coating composition for providing on surfaces which are predominantly of zinc or aluminum, a highly corrosion resistant chromate coating having excellent paint bonding characteristics when applied in accordance with the method of claim 1 which composition is an aqueous solution comprising zinc ions in an amount of at least 0.5 gram per liter, hexavalent chromium ions, calculated as CrO in an amount within the range of about 0.5 to 4.5 grams per liter, sulfate ions in an amount within the range of about 0.5 to about 40 grams per liter, and at least 0.15 gram per liter of a fluoride radical.
• composition as claimed in claim 6 wherein the zinc ions are present in an amount within the range of about 1 to 15 grams per liter, the hexavalent chromium ions, calculated as CrO are present in an amount within the range of about 1 to 3 grams per liter, the sulfate ions are present in an amount within the range of about 2 to 35 grams per liter, the fluoride radical is a complex fluoride radical which is present in an amount within the range of about 1 to 15 grams per liter, and the trivalent chrominum ions are present in an amount within the range of about 3 to 9 grams per liter.
• composition as claimed in claim 8 wherein the complex fluoride radical in the composition is selected from the group consisting of fluotitanates, fluoborates, fluosilicates, and fluoaluminates.
• composition as claimed in claim 8 wherein the pH of the coating solution is within the range of about 0.62 to about 3.5.
• composition as claimed in claim 10 wherein the pH of the solution is within the range of about 1.6 to about 2.5.

Landscapes

• 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)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23579241

Family Applications (1)

Country Status (5)

Cited By (6)

Families Citing this family (5)

Citations (9)

Family Cites Families (5)

• 1964
  • 1964-09-25 US US399365A patent/US3404046A/en not_active Expired - Lifetime
• 1965
  • 1965-08-30 BE BE668966D patent/BE668966A/xx unknown
  • 1965-09-10 DE DE1965M0066589 patent/DE1297952C2/de not_active Expired
  • 1965-09-18 JP JP40057353A patent/JPS4939385B1/ja active Pending
  • 1965-09-24 SE SE12418/65A patent/SE329070B/xx unknown

Patent Citations (9)

Also Published As

Similar Documents

Legal Events