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
  • C23C22/73—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
  • C23C22/05—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
  • C23C22/24—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 hexavalent chromium compounds
  • C23C22/33—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 hexavalent chromium compounds containing also phosphates

Definitions

• the water content of the layer is adjusted to within the range of about 4 to 20% by weight and an organic film forming resin is then applied to the watercontaining surface.
• the aqueous chromic acid-phosphoric acid coating material desirably also contains a filler, such as titanium dioxide- This invention relates to a method for coating metal surfaces to provide thereon a protective and/or paint base coating, and more particularly it relates to a method for coating surfaces of ferrous metal, zinc or aluminum, which is particularly adapted for application in a strip line process.
• prefinished metal, generally ferrous metal, zinc or aluminum, which is painted in the sheet or strip form and then fabricated.
• the prefinish applied may be a primer, a one or two coat finish paint or a laminate such as a plastic film or the like. Since the metal is fabricated after painting, severe requirements are placed both on the paint used, and to an even greater extent on the metal surface treatment before painting.
• the paint should be flexible yet tough and give corrosion resistance, while the surface treatment must provide excellent adhesion and form ability, and also good corrosion resistance.
• the equipment required for using these processes on a variety of metals normally includes a long series of treating stages, with those not needed for the particular metal in process being by-passed.
• hold tanks may be provided to store treating solutions not needed for a particular metal.
• an object of the present invention to provide a method for producing a paint base and/or protective coating on metal surfaces, which coating may be applied to aluminum, zinc and ferrous metal surfaces in the form of sheet and strip and overcomes the difiiculties of the prior art methods.
• a further object of the present invention is to provide a multimetal coating process which may be used in the prefinishing of painted sheet and strip to give a coating having good adhesion, physical properties, and resistance to salt fog.
• the present invention includes a process for treating a metal surface which comprises applying to the surface to be treated a layer of an aqueous coating mixture containing chromic acid and phosphoric acid, adjusting the water content of the thuscoated surface so as to provide thereon water in an amount within the range of about 4 to 20% by weight of the coating on the surface, thereafter, applying to the Water-containing surface an organic film forming material in an amount sufiicient to seal the surface and curing the coatings thus-formed on the surface.
• This method is found to be particularly applicable to use in strip lines and the coatings produced thereby are found to be excellent paint base and protective coatings.
• the aqueous coating solution which is applied to the metal surface desirably contains CrO in an amount within the range of about 4 to about 35% and H PO in an amount within the range of about 4 to about 35
• the CrO is present in the coating mixture in an amount within the range of about 6 to about 15% while the H PO is present in an amount within the range of about 6 to about 15%.
• the aqueous coating mixtures also desirably contain an inorganic filler material, which material may be present in the composition in amounts within the range of about 1 to about 40%, with amounts within the range of about 15 to about 25% being preferred.
• an inorganic filler material which material may be present in the composition in amounts within the range of about 1 to about 40%, with amounts within the range of about 15 to about 25% being preferred.
• Exemplary of such filler materials which may be used are titanium dioxide, colloidal silica, attapulgus clay, aluminum metal powder, zinc metal powder and the like. Additionally, it has been found that metal salts of organic fatty acids, such as zinc stearate, lead acetate, sodium acetate and the like, may also be used.
• the aqueous coating solution for use in the method of the present invention contains 8% by weight CrO 8% by weight H PO and 20% by weight of titanium dioxide.
• the aqueous coating solution may be applied to the metal surface to be treated in any convenient manner, as for example, by roller coating, spraying, flowing, immersion, and the like. Inasmuch as many strip lines have facilities for roller coating applications, in many instances this method of applying the coating solution is preferred. Accordingly, primary reference hereinafter will be made to applying the coating solution by roller coating. In such operations, the normal roller coating techniques, as are known to those in the art, may be used, and the solutions may be applied by either direct or reverse roll coating.
• the temperature of the chromic acid-phosphoric acid coating solutions have not been found to be critical. Accordingly, temperatures from room temperature, e.g., about 20 centigrade up to a boiling point of the solution may be used.
• the coating operation with these solutions is desirably carried out so that a coating weight within the range of about 5 to about 200 milligrams per square foot and preferably within the range of about 30 to about 60 milligrams per square foot is formed on the metal surface.
• the coating is applied evenly over the surface of the metal. In some instances, it also has been found to be desirable to ensure this even application by passing the coated surface through one or more rolls after the application of the coating solution.
• any excess coating solution is desirably removed from the surface and the water content of the thus-coated surface is adjusted so as to provide on the surface water in an amount within the range of about 4 to about 20% by weight of the coating on the surface.
• the water content is adjusted so as to provide water on the surface in an amount within the range of about 6 to about 10% by weight of the coating.
• This adjustment of the Water content of the surface may be effected in any convenient manner, and will depend upon the conditions under which the coating has been applied. Thus, for example, where the coating is applied under conditions of high-humidity, it may be necessary to remove water from the surface so as to bring the Water content within the 4 to by weight range.
• This may be done by drying the surface in any convenient manner, as for example by passing heated air over the surface.
• water may have to be added to the surface in order to bring the water content within the desired 6 to 20% by weight range.
• the addition of water to the surface may be effected in any convenient manner, as for example, by contacting the surface with moist air or steam.
• an organic film-forming material is applied to the wet surface.
• the surface to which the organic film forming material is applied has a moisture content within the range of about 4 to 20% by weight of the chromicphosphoric acid coating on the surface, the film adhesion and formability of the final coated metal surface are excellent.
• the moisture content of the surface is appreciably above 20% the corrosion resistance is greatly reduced and when it is less than about 4% the adhesion, formability and resistance to blistering on water immersion are reduced. Accordingly, it is quite important in the present process that the moisture content of the chromic acid-phosphoric acid coated surface be adjusted as has been indicated hereinabove and that this moisture content be maintained while the organic film forming material is applied on the surface.
• organic film forming material As with the chromic acid-phosphoric acid coating solution, various application techniques may be used in applying the organic film forming material, including spraying, roller coating, brushing, and the like.
• Various organic film forming materials may be used, such as alkyd resins, acrylic resins, epoxies, vinyls, urethanes, and other commonly used film forming resins. These materials may be pigmented or unpigmented, as is known in the art, and are applied in an amount sufficient to seal the metal surface being treated. In many instances, it has been found that coating weights of the film forming material as low as about 500 milligrams per square foot may be sufficient to effect the desired sealing of the metal surface.
• film forming material such as are sufficient to provide dry films of one mil thickness or even higher, may also be used if desired.
• film forming materials used may be in the form of paints, lacquers, enamels or the like, and are applied as solutions or dispersions of one or more of the above indicated resin materials in a suitable solvent.
• the film forming material on the coated metal surface is then cured.
• This curing may be effected by heating, baking or the like, depending upon the nature of the particular film forming material used. It is to be appreciated, that there is considerable latitude in the choice of the organic film forming material used and in the amounts which are applied to the metal surface.
• it is possible to obtain a treated metal surface having a finished top coat thereon by using a relatively heavy film of a film forming material which is a finish or top coat paint.
• a primed metal surface is obtained after the curing step which is then suitable for the application of the top or finish coat.
• the film-forming material applied may be unpigmented and applied in a relatively thin film, sufficient only to seal the metal surface.
• Such coatings have been found to be substantially equivalent to the primed coatings so that in many instances only a single top or finish coating is required on the surface. It has been found that with one coat of paint, however, there is sometimes a slight tinting, and a reduction in gloss of the paint film by the chromic acid. Thus, when light colors are used, it is preferable to use a very light coat of paint as the initial film former on the CrO -H PO mixture. Once this is baked subsequent paint coats are not affected.
• the process of the present invention may be used on various metal surfaces, including surfaces of aluminum, aluminum alloys which are predominantly aluminum, zinc, zinc alloys, which are prodaminantly zinc, and ferrous metal surfaces such as iron, steel and the like. Additionally, in some instances, metal surfaces other than those set forth hereinabove, may also be coated by this process.
• the present process then under a hot air blast which reduced the water conhas been found to be particularly applicable in the coating of metallic strip and sheet, and has particular utility in the coating of metal strip at relatively high line speeds.
• EXAMPLE 1 Clean steel panels, 4 inches by 10 inches, were treated which top coat was then cured by baking.
• the coating was effected by passing the panels through a roll coater, for a total of four passes, so as to work the coating into the surface of the panels. Excess coating solutions were then removed from the panels and the coating weights of the panels was determined to be about milligrams per square foot. Thereafter, the coated panels were humidified with a steam jet to provide a 40 water content on the surface of the panels of about 9% by weight of the coating. The panels were then immediately painted, while moist, with a white alkyd baking enamel, the enamel being applied by spraying in an EXAMPLE 3 the amounts indicated:
• A 2% CrO 8% H PO 20% TiO balance H O
• B 4% CrO 8% H PO 20% TiO balance H O
• C 6% CrO 8% H PO 20% TiO balance amount sufficient to provide a coating of about 600 milli- H O grams per square foot on the panel.
• top coated panels were then tested and gave excellent results in the knife (E) 8% CrO 6% H PO 20% TiO balance H2O -(F) 8% CrO 4% 11,190,, 20% TiO balance adhesion test and the water immersion test after immer- H 0 sion for 16 hours at centigrade. Additionally, in the c o 2% 0 20% 10 balance standard 5% salt fog test, the panels exhibited only from H2O 0 to 4 millimeters creepage after 117 hours in the test.
• EXAMPLE 2 A series of runs were made to compare the process of the present invention with commercially available processes for treating steel, galvanized steel (zinc) and aluminum. In these runs, panels of the three metals were treated by applying thereto a composition containing 12% CrO 8% H PO 20% TiO and 60% H O, using a forward roll coater at a surface speed of 200 feet/minute. The panels were then passed through two smoothing rolls and moist surface by spraying. The panels were cured bonding ability. tent of the surface to within the range of 6-10%. There- EXAMPLE 4 at 150 centigrade. The panels were then cooled and top used:
• Example 2 The procedure of Example 2 was repeated using the following coating compositions, which were applied in Coating weight in milligrams per sq.
• compositions were applied with a roll coater, as in Example 2, to panels of steel, galvanized steel and aluminum.
• the water content of the surface was adjusted to within the range of 6-10% using an air blast and a sealer film of a white alkyd enamel was applied to the baking for 5 minutes at centigrade, cooled and then top-coated with the same alkyd enamel.
• Example 3 The panels were then tested as in Example 2 and all showed good paint The procedure of Example 3 was repeated with the exception that the following coating compositions were A 23% cro 23% H3PO4, 33% TiO balance H2O (B) 28% CrO 28% H PO 33% TiO2, balance H O (C) 35% CrO 35% H PO balance H O
• the panels thus treated were sealed with vinyl and alkyd paint films, using both one and two coats after adjusting the surface moisture to 6-10% and the paint bond obtained was calculated. In each instance, good adhesion, formability and corrosion resistance were obtained.
• compositions were applied to steel test panels, the surface water adjusted to 610%. A film of a strip line paint applied and the combined coating cured 5 minutes at 150 C. The panels were then cooled and top coated with the same strip line paint. Evaluation of the paint bonds obtained was carried out and it was found that all compositions exhibited good paint bonding.
• the speed of the process can be readily varied without change in the time of the treatment and thus equipment length. Furthermore, the process is suited to the treatment of metals at very high speeds, the limiting speed being dependent mainly on the curing of the film former. Also the mixture is applied directly in the desired quantity so there is no depletion of active chemicals and consequent difliculty in control.
• a method for treating zinc, aluminum and ferrous metal surfaces which comprises applying tothe metal surface to be treated a layer of an aqueous coating mixture which consists essentially of from about 4 to by weight CrO and from about 4 to 35% by weight H PO adjusting the water-content of the thus-coated surface so as to provide thereon Water in an amount within the range of about 4 to about 20% by weight of the coating on the surface, thereafter, applying to the watercontaining surface an organic film-forming resin in an amount sufiicient to seal the surface and curing the coating thus-formed on the metal surface.
• aqueous coating mixture also contains an inorganic filler or metal salts of organic acids in an amount within the range of about 1 to about 40% by weight of the coating mixture.
• aqueous coating mixture is applied to the metal surface in an amount sufiicient to provide a coating weight within the range of about 5 to about 200 milligrams per square foot.
• organic, film forming resin is a resin selected from the group consisting of vinyl, alkyd and acrylic resins.

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
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• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
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• Application Of Or Painting With Fluid Materials (AREA)

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Citations (2)

• 1966
  • 1966-06-13 US US556890A patent/US3462319A/en not_active Expired - Lifetime
• 1967
  • 1967-06-03 DE DE19671646026 patent/DE1646026A1/de active Pending
  • 1967-06-05 BE BE699520D patent/BE699520A/xx unknown
  • 1967-06-07 CH CH805967A patent/CH475861A/de not_active IP Right Cessation
  • 1967-06-08 AT AT534467A patent/AT269588B/de active

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