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
  • C23C22/60—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 alkaline aqueous solutions with pH greater than 8

Definitions

• This invention relates to the art of forming protective coatings on the surfaces of zinc and zinc alloys from aqueous alkaline solutions.
• adherent corrosion resistance coatings are formed on the surface of zinc and zinc alloys by contacting the surfaces for a short time with an aqueous zinc oxide alkaline solution and a scale reducing amount of cyanuric acid.
• the aqueous alkaline solution contains at least two metal ions other than, and/ or in addition to alkali metal ions and a sufiicient quantity of complexing agent to maintain these ions in solution. It has been found that useful coatings are produced from the aqueous solutions of this invention when those solutions contain a wide range of variation of alkali strength, metallic ion concentration, complexing agent concentration, temperature and time of processing as well as type of application of the coating solution to the surface, each of which component and variations in operating conditions will be discussed in greater detail hereinafter.
• the alkalinity of the solution may be developed by using any of the commonly available alkaline compounds and alkaline salts, such as triethanola-mine and the alkali metal hydroxides, carbonates, phosphates, borates, silicates, polyphosphates, and pyrophosphates, or mixtures thereof as needed to give the desired pH. It has been found that the preferred operating conditions for the use of the solution of this invention include the use of a solution which has a pH numerically greater than about 11, and that better results are obtained from solutions having a pH in the range of 12.6 and 13.3.
• the above described coatings are obtained from solutions which contain extremely small quantities of metal ions other than the alkali metal ions and, in general, the color of the coating increases in intensity toward brown as the time of treatment is increased and as the concentration of metallic ion therein is increased, as the temperature of treatment is increased and as the alkali strength is increased.
• the solution should contain at least one metal ion other than an alkali metal ion, which is normally introduced with the alkaline salts, in order to produce a rate of coating formation and/or quality of coating which enables such coatings to function as superior bases for paint or other siccative coating. It has also been found that such other metal ion is incapable of functioning to increase the coating rate or coating formation mechanism unless it is sufficiently complexed by a complexing agent to dissolve that metal ion in the coating solution.
• the complexing chelating or sequestering agent functions to complex the metal ion other than the alkali metal ion and maintain the same dissolved in the coating solution.
• complexing, chelating, and sequestering agents have been found to be satisfactory.
• the inorganic complexacid, etc. the amino acids, such as glycine; the hydroxycarboxylic acids such as citric, gluconic, lactic, etc.; the hydroxyaldehydes such as acetyl acetone; the polyhydroxyaliphatic compounds such as sorbitol, 1,2-ethanediol; the phenolic carboxylic acids such as salicylic acid, phthalic acid; the amine carboxylic acids such as ethylene diamine tetraacetic acid; the polyamino acids such as diethalolaminomethane phosphate; the salts of lower molecular weight lignosulfonic acids such as derived from wood pulping processes such as sodium lignosulfonate.
• the amino acids such as glycine
• the hydroxycarboxylic acids such as citric, gluconic, lactic, etc.
• the hydroxyaldehydes such as acetyl acetone
• the polyhydroxyaliphatic compounds such as
• the proportion of complexing agent which should be present is an amount at least sufficient to completely complex the metal ion other than alkali metal ion, which is present. It will be apparent that as the concentration of metallic ion other than alkali metal ion increases the concentration of the complexing agent will also increase and since increasing quantities of certain of the complexing agent which are acidic in nature tends to reduce the effective alkali strength of the solution, it is preferred to employ the complexing agent in the form of neutral salts, particularly the alkali metal salts. Moreover, no advantage has been observed form the presence of concentrations of complexing agent in excess of that required to maintain the metal ion dissolved in the coating solution. Particularly good results have been obtained from the use of sodium hexahydroxyheptanoate, sodium gluconate and the sodium salt of ethylenediaminetetraacetic acid.
• the solutions of this invention may optionally include a compatible surface active agent and the presence of such a surface active agent is particularly advantageous when the surface to be coated is soiled with grease, oil, or the like.
• a compatible surface active agent is particularly advantageous when the surface to be coated is soiled with grease, oil, or the like.
• the only requirement for the surface active agent is that it be compatible with the other ingredients of the solution, both under normal storage conditions and under the elevated temperature application conditions, that is, the surface active agent should not cause precipitation or agglomeration of the metal ions which are present, cause gelling or itself precipitate or gel in the solutions. It has been found that there are nonionic, anionic and cationic wetting agents which are compatible in the solutions of this invention and when included up to about 5% of the solution, w./v., can be used.
• the process of this invention comprises the step of contacting the zinc or zinc alloy surface to be coated by spraying, dipping, brushing, or the like, at a temperature between ordinary room temperature and the boiling point of the solution and for a time period sufficient to produce the desired total coating.
• the preferred method of application in the formation of coatings adapted for use as a base for paint is spraying.
• Preferred conditions for continuous production which enables the formation of the desired coating in the least time involves the use of the solution at a temperature between about 90 F. and 200 F. for a time between about 2 seconds and about 60 seconds. Commercially satisfactory coatings have been obtained in about to seconds at about 100 F.l60 F.
• the complete process of this invention also includes the use of a subsequent dilute aqueous chromic acid rinse on the preliminarily formed coating of this invention.
• a suitable solution for this purpose is one which contains about 0.01% to 0.5% CrO w./v. or percent by weight per unit volume. When the chromic acid solution is relatively concentrated, it is preferred to remove the excess by squeezing the excess off with rolls.
• a preferred dilute rinse solution for the purpose of this invention is one which is disclosed and described in detail in copending application Ser. No. 230,729, filed Oct. 15, 1962, now US. Fat.
• the process of this invention has been found to be useful in forming coatings on the surfaces of pure zinc, electroplated zinc, hot-dipped zinc surfaces including hotdipped zinc containing small quantities of alloying ingredients such as aluminum, etc., and zinc alloys per se or electrodeposited zinc alloy surfaces.
• the surface to be coated includes iron or steel in addition to zinc or zinc alloy, such as a partially galvanized steel or iron base or a composite article which includes assembled steel or iron portions and zinc or zinc alloy portions, it has been found that such solutions of this invention are uniquely useful.
• the solutions of this invention are first applied by the procedures and temperature application conditions above specified to first clean the steel or iron portion of the article and clean and form a coating on the zinc or zinc alloy portion of the article, and this step is advantageously combined with a subsequent conventional phosphate coating step. It has been found that the coating formed on the zinc or zinc alloy portion of such surface is not removed by an aqueous acidic zinc phosphate or aqueous acidic alkali metal phosphate coating solution of any conventional constitution, and the cleaned steel or iron portion of the surface receives an adherent protective phoshate coating having at least equal corrosion resistance and utility as a base for paint as conventionally cleaned iron or steel surfaces. For the purposes of such modified process use it is satisfactory to employ aqueous acidic zinc phosphate solutions or aqueous acidic alkali metal phosphate solutions having any of the present-day conventional constitution, which are now well known to those skilled in the art.
• composition of the present invention may be prepared by mixing the alkali metal hydroxide with the zinc oxide in water which is heated to about F. To this mixture is added the sequestering agent plus the ions other than the alkali metal. This concentrate is then diluted with water which contains the scale reducing agent.
• a preferred scale reducing bath composition was prepared by mixing 897 grams of sodium hydroxide with 212 grams of zinc oxide in 1255 grams of water. This material was heated for a short period of time to about 180 F. This mixture then had added thereto 180 grams of Seqlene Fe 1300 (sodium hexahydroxyheptanoate), 74 grams of 40% Co(NO '6H O and 52 grams of Eighty-seven (87) grams of the above concentrate were added to 900 milliliters of water which had present therein 0.1% of cyanuric acid.
• the above example is an accelerated test to determine the scale decreasing capability of the additive.
• no zinc is introduced other than as the metal surface to be treated.
• the zinc in the bath is the result of the coating process.
• EXAMPLE II A preferred aqueous alkaline solution was prepared to contain 0.40% sodium hexahydroxyheptanoate, 0.40% cobalt added as cobalt nitrate 611 0, and 0.041% iron added as ferric nitrate 91-1 0. This bath contained 0.2% by weight cyanuric acid. The bath had a free alkalinity of 13.3 points (0.1 N sulfuric acid titrated with phenolphthalein as indicator). Electro-galvanized strip was sprayed with the above solution at 120 F. to produce a contact time of about seconds.
• cyanuric acid may be used in an amount ranging from 0.05% by weight to about 1% by weight, a preferred amount is from 0.1 to 0.3% by weight.
• An aqueous composition suitable for forming a coating on zinc and zinc alloy surfaces comprising:
• composition of claim 1 wherein said alkaline material is selected from the group consisting of triethanolamine and the alkali metal hydroxides, carbonates, phosphates, borates, silicates, polyphosphates, and pyrophosphates, or mixtures thereof.
• composition of claim 1 wherein the amount of alkaline material is sufficient to effect a composition pH of between 12.6 and 13.3.
• An aqueous composition suitable for forming a coating on zinc and zinc alloy surfaces comprising:
• At least one metal ion other than an alkali metal selected from the group consisting of silver, magnesium, cadmium, aluminum, tin, titanium, antimony, molybdenum, chromium, cerium, tungsten, manganese, cobalt, ferrous and ferric iron and nickel;
• composition of claim 4 wherein said alkaline material is selected from the group consisting of triethanolamine and the alkali metal hydroxides, carbonates, phosphates, borates, silicates, polyphosphates, and pyrophosphates, or mixtures thereof.
• composition of claim 4 wherein the amount of alkaline material is suflicient to effect a composition pH of between 12.6 and 13.3.
• composition of claim 4 wherein said cyanuric acid concentration is between about 0.05 and 1% by weight.
• composition of claim 7 wherein said cyanuric acid concentration is between about 0.1 and 0.3% by weight.
• a method of coating zinc and zinc alloy surfaces comprising contacting said surface with an aqueous composition comprising:
• alkaline material is selected from the group consisting of triethanolamine and the alkali metal hydroxides, carbonates, phosphates, borates, silicates, polyphosphates, and pyrophosphates, or mixtures thereof.
• a method of coating zinc and zinc alloy surfaces comprising contacting said surface with an aqueous composition comprising:
• At least one metal ion other than an alkali metal selected from the group consisting of silver magnesium, cadmium, aluminum, tin, titanium, antimony, molybdenum, chromium, cerium, tungsten, manganese, cobalt, ferrous and ferric iron and nickel;
• alkaline material is selected from the group consisting of triethanolamine and the alkali metal hydroxides, carbonates, phosphates, borates, silicates, polyphosphates, and pyrophosphates, or mixtures thereof.

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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)
• Paints Or Removers (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (10)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

Country Status (9)

Cited By (4)

Families Citing this family (3)

• 1971
  • 1971-09-07 US US00178504A patent/US3756864A/en not_active Expired - Lifetime
• 1972
  • 1972-08-11 DE DE2239581A patent/DE2239581C3/de not_active Expired
  • 1972-08-21 CA CA149,913A patent/CA983828A/en not_active Expired
  • 1972-08-24 FR FR7230156A patent/FR2152576B1/fr not_active Expired
  • 1972-08-28 BE BE788100A patent/BE788100A/xx unknown
  • 1972-08-29 GB GB4001972A patent/GB1362610A/en not_active Expired
  • 1972-09-06 IT IT28858/72A patent/IT967182B/it active
  • 1972-09-06 SE SE7211508A patent/SE388633B/sv unknown
  • 1972-09-07 JP JP47089133A patent/JPS526256B2/ja not_active Expired

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