Chromium-free surface treatment
Trivalent chromium passivate composition and process
Chromate coating of zinc surfaces
Composition and process for treating metals
Chromate passivating and storage stable concentrate solutions therefor
Composition and process for treating metals Patent #: 6758916
ApplicationNo. 10810546 filed on 03/26/2004
US Classes:148/247, Contains an atom of hafnium, titanium or zirconium (excludes activating composition)106/14.12, Phosphorus material106/14.44, Contains mixture of organic material and at least one inorganic material or elemental component thereof148/243, Liquid reactive coating composition utilized148/258, Contains an atom of chromium148/261, Contains an atom of arsenic, boron or metal atom other than alkali metal148/264, Contains an atom of chromium148/268, Contains an atom or boron, silicon or metal atom other than alkali metal427/384, Organic coating427/435, Metal base427/419.1, Metallic compound-containing coating427/419.2Oxide-containing coating
ExaminersPrimary: Green, Anthony
Attorney, Agent or Firm
Foreign Patent References
International ClassesC23C 22/07
DescriptionThis invention relates to processes for treating a metal surface to form a protective coating, or for treating a metal surface on which a protective coating has previously been formed and remains in place, with its protective qualities intact, onone part of the surface but is totally or partially absent from, or is present only in a damaged condition over, one or more other parts of the surface, so that its protective value in these areas of at least partial damage or absence has beendiminished. (Usually the absence or damage of the initial protective coating has been unintentional and has occurred as a result of such events as imperfectly uniform formation of the initial protective coating, mechanical damage of the initialprotective coating, spotty exposure of the initially coated surface to solvents for the initial protective coating, or the like. The absence or damage of the initial protective coating may be intentional, however, as when holes are drilled in a contactsurface, for example, or when untreated parts are attached to and therefore become part of a previously coated surface.) Particularly if the surface in question is large and the damaged or untreated area(s) are relatively small, it is often moreeconomical to attempt to create or restore the full protective value of the original coating primarily in only the absent or damaged areas, without completely recoating the object. Such a process is generally known in the art, and will be brieflydescribed herein, as "touching up" the surface in question. This invention is particularly well suited to touching up surfaces in which the original protective coating is a conversion coating initially formed on a primary metal surface, moreparticularly a primary metal surface consisting predominantly of iron, aluminum, and/or zinc.
An alternative or concurrent object of this invention is to provide a process for protectively coating metal surfaces that were never previously coated. Other concurrent or alternative objects are to achieve at least as good protective qualitiesin the touched up areas as in those parts of the touched up surfaces where the initial protective coating is present and undamaged; to avoid any damage to any pre-existing protective coating from contacting it with the touching up composition; and toprovide economical touching up process. Other objects will be apparent to those skilled in the art from the description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, a numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word"about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, throughout this description, unless expressly stated to the contrary: percent, "parts of", and ratio values are byweight; the term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two ormore of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ bychemical reactions specified in the description, and does not necessarily preclude other chemical interactions among the constituents of a mixture once mixed; specification of materials in ionic form additionally implies the presence of sufficientconstituents to produce electrical neutrality for the composition as a whole (any counterions thus implicitly specified should preferably be selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise suchcounterions may be freely selected, except for avoiding counterions that act adversely to the objects of the invention); and the term "mole" and its grammatical variations may be applied to elemental, ionic, and any other chemical species defined bynumber and type of atoms present, as well as to compounds with well defined molecules.
SUMMARY OF THE INVENTION
It has been found that excellent coating and/or touching up quality, particularly for corrosion resistance on previously untreated areas and corrosion resistance in combination with a conversion coating, can be achieved by: (I) covering the areasto be touched up with a layer of a liquid composition that comprises, preferably consists essentially of, or more preferably consists of, water and: (A) a component of fluorometallate anions, each of said anions consisting of: (i) at least four fluorineatoms; and (ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron; and, optionally, one or both of (iii) at least one ionizable hydrogen atom; and (iv) at least one oxygenatom; (B) a component of phosphorus-containing inorganic oxyanions and/or phosphonate anions; and (C) a component of oxidizing agent or agents that are not part of either of immediately previously recited components (A) and (B) and are not chromium(III)cations; and, optionally, one or more of the following components: (D) chromium(III) cations; (E) a component of free fluoride ions that are not part of any of immediately previously recited components (A) through (D); (F) a component of surfactantmolecules that are not part of any of immediately previously recited components (A) through (E); (G) an acidifying component that is not part of any of the immediately previously recited components (A) through (F); and (H) a viscosity increasingcomponent that is not part of any of the immediately previously recited components (A) through (G); and subsequently (II) drying into place over the surface the liquid layer formed in step (I).
It should be understood that the components listed need not necessarily all be provided by separate chemicals. For example, it is preferred that the fluorometallate anions and phosphorous-containing anions both be added in the form of thecorresponding acids, thereby also providing at least some, and usually all, of optional acidifying component (G).
Various embodiments of the invention include processes for treating surfaces as described above, optionally in combination with other process steps that may be conventional per se, such as precleaning, rinsing, and subsequent further protectivecoatings over those formed according to the invention, compositions useful for treating surfaces as described above, and articles of manufacture including surfaces treated according to a process of the invention.
DETAILED DESCRIPTION OF THEINVENTION
For a variety of reasons, it is preferred that compositions used according to the invention as defined above should be substantially free from many ingredients used in compositions for similar purposes in the prior art. Specifically, it isincreasingly preferred in the order given, independently for each preferably minimized component listed below, that these compositions, when directly contacted with metal in a process according to this invention, contains no more than 1.0, 0.35, 0.10,0.08, 0.06, 0.04, 0.02, 0.01, 0.005, 0.002, 0.001, 0.0005, or 0.0002 percent of each of the following constituents: dispersed (in this instance not including truly dissolved) silica and/or silicates; ferricyanide; ferrocyanide; sulfates and sulfuricacid; anions containing molybdenum or tungsten; alkali metal and ammonium cations; pyrazole compounds; sugars; glyconic acid and its salts; glycerine; α-glucoheptanoic acid and its salts; and myoinositol phosphate esters and salts thereof.
A working composition for use in a process according to this invention preferably has a concentration of at least, with increasing preference in the order given, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 4.8 millimoles of fluorometallateanions, component (A), per kilogram of total working compositions, this unit of concentration being freely applicable hereinafter to any other constituent as well as to fluorometallate anions and being hereinafter usually abbreviated as "mM/kg"; and ifthe maximum corrosion protection from a single treatment with a composition used in a process according to the invention is desired as it often is, this concentration of fluorometallate anions more preferably is at least, with increasing preference inthe order given, 6.0, 7.0, 8.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, or 24.0 mM/kg. Independently, in a working composition, the concentration of fluorometallate ions preferably, at least for economy, isnot more than, with increasing preference in the order given, 240, 150, 100, 80, 60, 50, 45, 40, 35, 30, or 27 mM/kg, and if the working composition is intended for use in a process in which at least two treatments according to the invention will beapplied to the substrate, this concentration of fluorometallate anions still more preferably is not more than, with increasing preference in the order given, 20, 15, 12, 10, 8.0, 7.0, 6.5, 6.0, 5.5, or 5.1 mM/kg.
Independently of their concentration, the fluorometallate anions preferably are fluorosilicate (i.e., SiF6-2), fluorotitanate (i.e., TiF6-2) or fluorozirconate (i.e., ZrF6-2), more preferably fluorotitanate orfluorozirconate, most preferably fluorozirconate.
Component (B) as defined above is to be understood as including all of the following inorganic acids and their salts and acid salts that may be present in the composition: hypophosphorous acid (H3PO.sub.2), orthophosphorous acid(H3PO.sub.3), polyphosphoric acid (H4P.sub.2O.sub.7), orthophosphoric acid (H3PO.sub.4), tripolyphosphoric acid (H5P.sub.3O.sub.10), and further condensed phosphoric acids having the formula HA 2P4O.sub.3x 1, where x is apositive integer greater than 3. Component (B) also includes all phosphoric acids and their salts.
Generally, inorganic phosphates, particularly orthophosphates, phosphites, hypophosphites, and/or pyrophosphates, especially orthophosphates, are preferred for component (B) because they are more economical. Phosphonates are also suitable andmay be advantageous for use with very hard water, because the phosphonates are more effective chelating agents for calcium ions. Acids and their salts in which phosphorous has a valence less than five may be less stable than the others to oxidizingagents and are therefore less preferred.
A composition according to the invention preferably contains at least, in increasing preference in the order given, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, or 0.70 parts, measured as its stoichiometric equivalents as H3PO.sub.4 ofcomponent (B) per thousand parts of total composition, a concentration unit that may be freely used hereinafter for other constituents and is hereinafter usually abbreviated as "ppt". Independently, in a working composition used in a process accordingto the invention, the concentration of component (B), measured as its stoichiometric equivalent as H3PO.sub.4, preferably is not more than, in increasing order of preference, 10, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, 1.00, 0.90, or 0.80 ppt.
The oxidizing agent, component (C), preferably is selected from hydrogen peroxide; alkyl and other substituted peroxides; materials containing hexavalent chromium, such as chromates and dichromates; manganates and permanganates; chlorates andperchlorates; iodates and periodates; nitrates; bromates and perbromates, molybdenum, vanadates, and all of the acids corresponding to all of the previously listed anions in this sentence. Unless the use of hexavalent chromium as at least part ofoxidizing agent component (C) is barred because of fears of pollution and/or personnel hazard, the use of hexavalents chromium is strongly preferred. More particularly, the amount of hexavalent chromium present in a working composition for use accordingto the invention, an amount which may readily be determined analytically by means known in the art, preferably is at least, with increasing preference in the order given, 0.30, 0.50, 0.70, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, or 2.70 grams ofhexavalent chromium per liter of total working composition, a unit of measure which may be applied hereinafter to other components, and which is hereinafter usually abbreviated as "g/l." Independently, the concentration of hexavalent chromium is aworking composition used in a process according to this invention preferably is not greater than, with increasing preference in the order given, 30, 25, 20, 15, 10, 8, 6, 5.0, 4.0, 3.5, 3.3, 3.1, or 2.9 g/l.
Hexavalent chromium may be applied to the working composition from any water soluble source, including numerous available dichromate and chromate salts. However, at least for reasons of economy, the hexavalent chromium preferably is supplied asthe chemical substance with the formula CrO3, usually named "chromic acid" or "chromium trioxide".
If the oxidizing agent component does not include hexavalent chromium, its "oxidizing power" should be adjusted to fall within the same range as is achieved in an alternative working composition by use of preferred amounts of hexavalent chromiumas indicated above, together with all other necessary and preferred constituents as described herein. The oxidizing power for this purpose may be conveniently measured by the electrical potential of an inert metal electrode, such as a platinumelectrode, that is in physical contact with the liquid for which the oxidizing power is to be measured. The electrical potential of the inert metal electrode is measured by comparison with a reference electrode of known conventionally establishedpotential, by means known to those skilled in the art.
When oxidizing agent component (C) includes hexavalent chromium as it preferably does, optional component (D) of chromium(III) cations preferably is also used. At least one reason for this preference is that the presence of chromium (III)cations is useful in preventing, or at least diminishing, leaching by water of the hexavalent chromium content of the coating formed in a process according to this invention when hexavalent chromium is a part of the treatment composition used. Thesource of the chromium(III) ions may be any soluble or solubilizable source whose counterions do not interfere with the objects of the invention. Soluble salts include the acetate, bromide hexahydrate, chloride hexahydrate, iodide, nitrate oxalate orsulfate of chromium (III); complexes such as hexammine chromium(III) chloride, and others which are chemically compatible with the coating composition. However, at least in part for economy, the chromium(III) cations present in a composition used in aprocess according to this invention preferably are desired from an in situ reduction of part of a source of hexavalent chromium added to provide, from its unreduced portion, at least part of composition (C). Suitable reducing agents are well known tothose skilled in the art, with organic compounds, particularly inexpensive carbohydrates such as sugar and starch, normally preferred.
The concentration of chromium(III) cations is preferably at least, in increasing order of preference, 0.10, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.60, or 1.70 g/l. The ratio of hexavalent chromium atoms to trivalent chromium atoms in a compositionto be used in a process according to this invention is preferably at least, in increasing preference in the order given, 0.50:1.00, 0.75:1.00, 1.00:1.00, 1.10:1.00, 1.20:1.00, 1.30:1.00, 1.40:1.00, 1.45:1.00, or 1.50:1.00 and independently preferably isnot more than, with increasing preference in the order given, 20:1.00, 10:1.00, 5:1.00, 3.0:1.00, 2.5:1.00, or 2.0:1.00. The total concentration of chromium atoms of any valence in a working composition according to the invention is preferably at least,with increasing preference in the order given, 0.45, 0.60, 0.80, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, 3.8, 4.0, or 4.4 g/l, and independently, primarily for reasons of economy, is preferably not more than, with increasing preference in the order given, 50, 35,20, 14, 10, 9.0, 8.0, 7.0, 6.5, 6.0, 5.5, 5.0, or 4.6 g/l. Preferred amounts of chromium(III) cations in a working composition to be used according to the invention may be determined by subtracting from these numbers the values given above for theconcentration of hexavalent chromium.
If the fluorometallate anions concentration exceeds 4.8 mM/kg in a composition to be used in a process according to this invention, optional component (E) of free fluoride ions is preferably included also, unless the composition is to be usedwithin a few days of having been made. Otherwise, formation of a precipitate during storage of the composition is likely. This component may be supplied to the composition by hydrofluoric acid or any of its partially or completely neutralized saltsthat are sufficiently water soluble. At least for economy, component (E) is preferably supplied by aqueous hydrofluoric acid, and independently preferably is present in a concentration that is at least, with increasing preference in the order given,0.10, 0.30, 0.50, 0.60, 0.70, 0.80, or 0.90 ppt of its stoichiometric equivalent as HF. Independently, in a working composition to be used in a process according to the invention, the concentration of component (E), measured as its stoichiometricequivalent as HF, preferably is not more than, with increasing preference in the order given, 10, 8.0, 6.0, 4.0, 3.0, 2.0, 1.5, 1.3, or 1.1 ppt.
Component (F), if used, is chosen from anionic surfactants, such as salts of carboxylic acids, alkylsulphonates, alkyl-substituted phenylsulphonates; non-ionic surfactants, such as alkyl-substituted dephenylacetylenic alcohols and nonylphenolpolyoxyethylenes; and cationic surfactants such as alkylammonium salts; all of these may and preferably do contain fluorine atoms bonded directly to carbon atoms in their molecules. Each molecule of a surfactant used preferably contains a hydrophobeportion that (i) is bonded by a continuous chain and/or ring of covalent bonds; (ii) contains a number of carbon atoms that is at least, with increasing preference in the order given, 10, 12, 14, or 16 and independently preferably is not more than, withincreasing preference in the order given, 30, 26, 22, or 20; and (iii) contains no other atoms except hydrogen, halogen, and ether-bonded oxygen atoms. Component (F) is most preferably a fluorinated alkyl ester such as FLUO-RAD™ FC 430, a materialcommercially supplied by Minnesota Mining and Manufacturing Co.
A working composition according to the invention preferably contains, with increasing preference in the order given, at least 0.010, 0.030, 0.050, 0.070, 0.080, 0.090, or 0.100 ppt of component (F) and independently preferably, primarily forreasons of economy, contains not more than, with increasing preference in the order given, 5.0, 2.5, 1.30, 0.80, 0.60, 0.40, 0.40, 0.30, 0.20, 0.18, 0.15, 0.13, or 0.11 ppt of component (F).
The pH of a composition used according to the invention preferably is at least, with increasing preference in the order given, 0.10, 0.30, 0.50, 0.70, 0.90, 1.10, 1.20, 1.30, 1.40, 1.50, 1.55, or 1.60 and independently preferably is not morethan, with increasing preference in the order given, 5.0, 4.0, 3.5, 3.0, 2.90, 2.80, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, 2.10, 2.00, 1.90, 1.80, or 1.70. Ordinarily, a preferred pH will result automatically from use of preferred concentrations ofhexavalent chromium, phosphate ions, fluorometallate anions, and free fluoride ions supplied to the composition from preferred acidic sources as already noted. If, however, in some particular instance, a preferred pH value is not achieved in thismanner, other acidifying agents are well known in the art and may be used as optional component (G). This component, however, is normally preferably omitted, at least for economy.
Dilute compositions, within these preferred ranges, that include the necessary active ingredients (A) through (C) only may have inadequate viscosity to be self-supporting in the desired thickness for touching up areas that can not be placed in asubstantially horizontal position during treatment and drying; if so, one of the materials known in the art, such as natural gums, synthetic polymers, colloidal solids, or the like should be used as optional component (H), as is generally known in theart, unless sufficient viscosity is provided by one or more of other optional components of the composition. If the characteristic treatment composition is to be applied in a process according to the invention by use of a saturated felt or likematerial, component (H) is rarely needed and usually is preferably omitted, because most viscosity increasing agents are susceptible to being at least partially filtered out of the treatment composition by applicators of this type.
A working composition according to the invention may be applied to a metal workpiece and dried thereon by any convenient method, several of which will be readily apparent to those skilled in the art. For example, coating the metal with a liquidfilm may be accomplished by immersing the surface in a container of the liquid composition, spraying the composition on the surface, coating the surface by passing it between upper and lower rollers with the lower roller immersed in a container of theliquid composition, contact with a brush or felt saturated with the liquid treatment composition, and the like, or by a mixture of methods. Excessive amounts of the liquid composition that might otherwise remain on the surface prior to drying may beremoved before drying by any convenient method, such as drainage under the influence of gravity, passing between rolls, and the like.
A particularly advantageous method of application of the treatment liquid in a process according to the invention makes use of an applicator as disclosed in U.S. Pat. No. 5,702,759 of Dec. 30, 1997 to White et al., the entire disclosure ofwhich, except for any part that may be inconsistent with any explicit statement herein, is hereby incorporated herein by reference.
The temperature during application of the liquid composition may be any temperature within the liquid range of the composition, although for convenience and economy in application, normal room temperature, i.e., from 20-27° C., is usuallypreferred.
Preferably the amount of compositions applied in a process according to this invention is chosen so as to result, after drying into place, in at least as good corrosion resistance for the parts of the surface treated according to the invention asin the parts of the same surface where the initial protective coating is present and a process according to the invention has not been applied. Ordinarily, for most common protective phosphate and chromate conversion coatings as initial protectivecoatings, such protection will be achieved if the total add-on mass (after drying) of the coating applied in a process according to the invention is at least, with increasing preference in the order given, 0.005, 0.010, 0.015, 0.020, 0.025, 0.030, 0.035,0.040, 0.045, 0.050, 0.055, or 0.060 grams per square meter of surface coated (hereinafter usually abbreviated as "g/m2"). Independently, at least equal corrosion resistance ordinarily will be achieved even if the add-on mass is not, and thereforefor reasons of economy the add-on mass preferably is not greater than, with increasing preference in the order given 1.00, 0.70, 0.50, 0.30, 0.20, 0.15, 0.10, 0.090, 0.085, 0.080, or 0.075 g/m2.
The add-on mass of the protective film formed by a process according to the invention may be conveniently monitored and controlled by measuring the add-on weight or mass of the metal atoms in the anions of component (A) as defined above, or ofchromium when that is part of component (C) of the treatment composition used, except in the unusual instances when the initial protective coating and/or the underlying metal substrate contains the same metal element(s). The amount of these metal atomsmay be measured by any of several conventional analytical techniques known to those skilled in the art. The most reliable measurements generally involve dissolving the coating from a known area of coated substrate and determining the content of themetal of interest in the resulting solution. The total add-on mass can then be calculated from the known relationship between the amount of the metal in component (A) and the total mass of the part of the total composition that remains after drying. However, this method is often impractical for use with this invention, because the area touched up is not always precisely defined. A more practical alternative is generally provided by small area X-ray spectrographs that, after conventionalcalibration, directly measure the amount(s) per unit area of individual metallic element(s) present in a coating, free from almost all interferences except the same elements present in other changes on, or in a thin layer near the surface of, theunderlying metal surface itself.
In many instances sufficiently precise control of the amount of coating used can be determined visually from the color of the area coated, because most preferred compositions for use according to the invention are fairly strongly colored. Unlessthe surface to be treated happens to be the same or a similar color, the amount of active ingredients can therefore be estimated by the intensity of the color of the liquid film formed in a process according to the invention.
The effectiveness of a treatment according to the invention appears to depend predominantly on the total amounts of the active ingredients that are dried in place on each unit area of the treated surface, and on the nature of the activeingredients and their ratios to one another, rather than on the concentration of the acidic aqueous composition used, and the speed of drying has not been observed to have any technical effect on the invention, although it may well be important foreconomic reasons. If practical in view of the size of the object treated and the size of the areas of the object to be treated, drying may be speeded by placement of the surface to be treated, either before or after application to the surface of aliquid composition in a process according to the invention, in an oven, use of radiative or microwave heating, or the like. If speed of treatment is desired, but placing the entire object in an oven is inconvenient, a portable source of hot air orradiation may be used in the touched up area(s) only. In either instance, heating the surface before treatment is preferred over heating after treatment when practical, and prewarming temperatures up to at least 65° C. may be satisfactorilyused. If ample time is available at acceptable economic cost, a liquid film applied according to this invention often may simply be allowed to dry spontaneously in the ambient atmosphere with equally good results insofar as the protective quality of thecoating is concerned. Suitable methods for each circumference will be readily apparent to those skilled in the art.
Preferably, the surface to be treated according to the invention is first cleaned of any contaminants, particularly organic contaminants and foreign metal fines and/or inclusions. Such cleaning may be accomplished by methods known to thoseskilled in the art and adapted to the particular type of substrate to be treated. For example, for galvanized steel surfaces, the substrate is most preferably cleaned with a conventional hot alkaline cleaner, then rinsed with hot water and dried. Foraluminum, the surface to be treated most preferably is first contacted with a conventional hot alkaline cleaner, then rinsed in hot water, then, optionally, contacted with a neutralizing acid rinse and/or deoxidized, before being contacted with an acidaqueous composition as described above. Ordinarily, cleaning methods suitable for the underlying metals will also be satisfactory for any part of the initial protective coating that is also coated in a process according to the invention, but care shouldbe taken to choose a cleaning method and composition that do not themselves damage the protective qualities of the initial protective coating in areas that are not to be touched up. If the initial protective coating is thick enough, the surface can besatisfactorily cleaned by physically abrading, as with sandpaper or another coated abrasive, the area(s) to be touched up and any desired overlap some where the initial protective coating is still in place around the damaged areas to be touched up. Theswarf may then be removed by blowing, brushing, rinsing, or with attachment to a cleaning tool, such as a moist cloth. It has been found that, when dry abrasion is used as the last preparatory cleaning method, the corrosion resistance of the coatingusually will be less than optimal and the coating will appear smutty. However, dry abrasion followed by rinsing is a satisfactory and often preferred cleaning method. One indication that the surface is sufficiently clean is that a film of water sprayedon the surface will dry without beading.
After the preparatory cleaning, the surface may be dried by absorption of the cleaning fluid, evaporation, or any suitable method known to those skilled in the art. Corrosion resistance is usually less than optimal when there is a delay betweenthe preparatory cleaning, or cleaning and drying, and the coating of the surface. The time between cleaning, or cleaning and drying, and coating the surface should be no more than, in increasing order of preference, 48, 24, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0,0.50, 0.25, or 0.1 hours.
Usually, it is preferable, as a precaution during a touch up process according to the invention, to apply the composition used for touching up not only to obviously bare metal or obviously damaged areas of the initial protective coating, but alsoover a transition or overlap zone of apparently undamaged initial protective coating adjacent to such areas that obviously need touching up. With increased preference in the order given, such a transition zone has a width that is at least 0.2, 0.5, 0.7,1.0, 1.5, or 2.0 millimeters and independently preferably, primarily for reasons of economy, is not more than, with increasing preference in the order given, 25, 20, 15, 10, 8.0, 6.0, 5.0, or 3.0 millimeters.
Virtually any kind of initial protective coating can be touched up effectively for many purposes by a process according to this invention. In particular, but without limitation, conversion coatings produced on underlying metal according to theteachings of any one of the following U.S. Patents, the disclosures of all of which, except to any extent that they may be inconsistent with any explicit statement herein, are hereby incorporated herein by reference, may be effectively touched up by aprocess according to this invention: U.S. Pat. No. 5,769,667 of Jun. 23, 1998 to Dolan; U.S. Pat. No. 5,700,334 of Dec. 23, 1997 to Ishii et al; U.S. Pat. No. 5,645,650 of Jul. 8 1997 to Ishizaki et al.; U.S. Pat. No. 5,683,816 of Nov. 4,1997 to Goodreau; U.S. Pat. No. 5,595,611 of Jan. 21, 1997 to Boulos et al; U.S. Pat. No. 5,551,994 of Sep. 3, 1996 to Schriever; U.S. Pat. No. 5,534,082 of Jul. 9, 1996 to Dollman et al.; U.S. Pat. No. 5,507,084 of Apr. 16, 1996 to Ogino etal.; U.S. Pat. No. 5,498,759 of Mar. 12, 1996 to Nakada et al.; U.S. Pat. No. 5,498,300 of Mar. 12, 1996 to Aoki et al.; U.S. Pat. No. 5,487,949 of Jan. 30, 1996 to Schriever, U.S. Pat. No. 5,472,524 of Dec. 5, 1995; U.S. Pat. No. 5,472,522of Dec. 5, 1995 to Kawaguchi et al; U.S. Pat. No. 5,452,884 of Oct. 3, 1995; U.S. Pat. No. 5,451,271 of Sep. 19, 1995 to Yoshida et al.; U.S. Pat. No. 5,449,415 of Sep. 19, 1995 to Dolan; U.S. Pat. No. 5,449,414 of Sep. 12, 1995 to Dolan; U.S. Pat. No. 5,427,632 of Jun. 27, 1995 to Dolan; U.S. Pat. No. 5,415,687 of May 16, 1995 to Schriever; U.S. Pat. No. 5,411,606 of May 2, 1995 to Schriever; U.S. Pat. No. 5,399,209 of Mar. 21, 1995 to Suda et al.; U.S. Pat. No. 5,395, 655 of Mar. 7, 1995 to Kazuyuki et al.; U.S. Pat. No. 5,391,239 of Feb. 21, 1995 to Boulos; U.S. Pat. No. 5,378,392 of Jan. 3, 1995 to Miller et al.; U.S. Pat. No. 5,366,567 of Nov. 22, 1994 to Ogino et al.; U.S. Pat. No. 5,356,490 of Oct. 18, 1994 toDolan et al.; U.S. Pat. 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A process according to this invention is particularly advantageously applied to touching up a surface in which the undamaged parts are protected by a coating selected from the group consisting of a phosphate conversion coating, a chromateconversion coating, and a conversion coating produced by contacting a predominantly aluminiferous or a predominantly zinciferous surface with an acidic treating solution comprising at least one of fluorosilicate, fluorotitanate, and fluorozirconate.
In addition, of course, metal surfaces with any other type of previously applied protective coating or without any previous deliberately applied coating can be coated in a process according to the invention.
The practice of this invention may be further appreciated by consideration of the following, non-limiting, working examples.
In this group, a preferred type of base solution for making up working compositions for use in a process according to the invention was first prepared as follows: 0.94 part of pearl cornstarch was slurried together with 8.00 parts of deionized(hereinafter usually abbreviated as "DI") water. In a separate container, 300 parts of DI water, 8.56 parts of chromic acid (i.e., CrO3) crystals, and 1.00 part of an aqueous solution containing 75% of H3PO.sub.4 were mixed together. Thepreviously prepared slurried starch mixture was then added to the other mixture, and all of the thus formed new mixture was heated to boiling temperature, with stirring and reflux condensation of evaporating water, and boiled for 90 minutes to assurecomplete reaction of the starch. Later analysis showed that 5.2 parts out of the originally added 8.56 parts of chromic acid remained in a hexavalent form after this reaction (and any reaction that may have occurred with other ingredients added later tomake a complete working composition for use according to this invention). The remainder of the initially added chromium is presumed to have been reduced to chromium(III) cations that remain dissolved in the solution. (The only significant productderived from the starch under these reaction conditions is believed to be carbon dioxide that escapes into the atmosphere, but if any non-volatile product is formed and remains in the product after boiling, any such residue from the starch does not harmthe use of the product or essentially change the nature of the invention.)
TABLE-US-00001 TABLE 1 Concentration in Ppt of Ingredient Ingredient in Working Composition H2ZrF.sub.6 5.0 1.00 H2SiF.sub.6 5.0 1.00 FeF3 0.093 HF 1.00 0.50 0.10 H2O.sub.2 0.15 H2MoO.sub.4 5.0 1.00
The base solution prepared as described in the immediately preceding paragraph was used to form candidate working position according to the invention by adding one of the materials noted in Table 1 to a portion of this base solution, which isdiluted, using D1 water, along with these additions so that the "parts" of ingredients, other than starch and the fraction of the initially added chromic acid modified by reactions with starch, that were used to make the base solution, as specifiedabove, are present in 1000 total parts of the final working composition. (All of the chromium atoms contained in the chromic acid originally used are believed to remain in the solution, with these atoms not having been reduced to a trivalent formremaining as hexavalent chromium atoms, which may be present as unchanged chromic acid and/or as chromate and/or condensed chromate anions. All of the forms of hexavalent chromium present in these solutions are believed to be substantially equallyeffective in forming a protective coating in a process according to this invention.)
Surfaces of conventional rectangular (7.6×25 centimeters) sheet test pieces of Types 7075, 6061, and/or 2024-T3 aluminum were treated according to the invention, after preparatory cleaning and other treatment as follows.
Each panel was placed on a non-slip surface of plastic webbing over absorbent towels, and a rectangular (5.1×7.6 centimeters) Scotch-Brite™ 96 Very Fine green lofty non-woven coated abrasive pad, saturated with water, was used touniformly scrub the panel lengthwise, using long straight strokes of slight to moderate pressure. The pad was then rinsed well with clean tap water (and left water-saturated) and, using the same side and end of the pad, the panel was rubbed with similarstrokes in the crosswise direction. The pad was rinsed again and, using the same side of the pad but the fresh end, the panel was scrubbed in the lengthwise direction once again with similar strokes. The panel was then rinsed briefly with water andsubsequently wiped dry with a fresh absorbent paper wiper. The panel was set aside and the pad rinsed well. (The opposite side of the pad was used in the same way on the next panel, and the pad was then discarded).
After two panels had been cleaned and dried, a first treatment according to the invention was applied over the cleaned panel surface in the lengthwise direction, from an applicator as described in U.S. Pat. No. 5,702,759, using even strokeswith a 50% overlap. Moderate and even pressure (not nearly enough to activate the valve in the applicator) was used, because using such moderate and even pressure facilitates forming an even coating that has little tendency to dewet. While this coatwas drying, another two panels were usually cleaned as described in the immediately preceding paragraph. Usually by the time two more panels had been cleaned, the once coated panels were ready for their second coat. The second coat was applied in thecrosswise direction, and then the two freshly cleaned panels were given their first coat.
The treated panels were subjected to salt spray testing and were visually rated qualitatively only for corrosion resistance. The corrosion resistance decreased from the top to the bottom of Table 1 according to this rating, but all of the panelswould be satisfactory for many uses.
In this group, the more promising additives from Group 1 were investigated more thoroughly, along with an organic polymer resin and some combinations of these materials. The base solution was the same as for Group 1, except for the addition ofFLUO-RAD™ 430 in an amount corresponding to 0.1 ppt of the final working composition, and the additional constituent or constituents are shown in Table 2. In this table, the abbreviation "AC-73" means RHOPLEX™ AC-73, an acrylic polymer emulsioncommercially supplied by Rohm & Haas and reported by its supplier to contain 46-47% of ultimate resin solids.
TABLE-US-00002 TABLE 2 Identifying Number Content of H2ZrF.sub.6 Content of HF Content of AC-73 1 1.0 ppt 0 0 2 5.0 ppt 0 0 3 1.0 ppt 1.0 ppt 0 4 1.0 ppt 0 20 ppt 5 5.0 ppt 0 20 ppt 6 5.0 ppt 1.0 ppt 20 ppt 7 3.0 ppt 0 0 8 3.0 ppt 1.0 ppt 09 0 0 10 10 7.5 ppt 1.0 ppt 0 11 10 ppt 1.0 ppt 0 12 5.0 ppt 0.10 ppt 0 13 5.0 ppt 0.25. ppt 0 14 5.0 ppt 0.50 ppt 0 15 5.0 ppt 0.75 ppt 0
Test substrates were conventional flat panels of Type 2024 aluminum alloy supplied by Advanced Coating Technologies ("ACT") and Aluminum Company of America ("ALCOA") or of Type 7075 aluminum alloy supplied by ALCOA or Kaiser Aluminum Company("Kaiser"). These were prepared and treated in the same manner as in Group 1, except that a second treatment according to the invention was applied on only half of each substrate panel, so that the effects of both single and double treatments could beevaluated on each panel. The coated panels were then subjected for 504 hours to salt spray testing according to American Society for Testing and Material Procedure B 117, except that the tested panels were maintained at an angle 6° from verticalduring their exposure as prescribed by MIL-C-5541E. Results are shown in Table 3.
TABLE-US-00003 TABLE 3 Rating after 504 Hours of Salt Spray for Substrate: ACT 2024 ALCOA ALCOA Kaiser 7075 with: 2024 with: 7075 with: with: Identification 1 2 1 2 1 2 1 2 Number Coat Coats Coat Coats Coat Coats Coat Coats 1 10% 1% D 5% D Good10% 1% D 5% D 1% D, SP D D, P 2 5% Good 5% D Good 5% D Good 5% D Good D, SP 3 1% D Good Good Good 2% D Good 2% D Good 4 1% D Good 2% D Good 5% D Good 2% D Good 5 3% D Good 2% D Good 5% Good Good Good D, P 6 5% D Good 2% D Good SP Good Good Good 7 20%Good Good Good SP Good Good Good D 8 2% D Good 1% D Good SP Good Good Good 9 10% Good 5% D Good 1% D Good 5% D Good D 10 2% D Good 1% D Good 0.5% Good 2% D Good D 11 Good Good Good Good SP Good 2% D Good 12 1% D Good 3% D Good SP Good Good Good 13 GoodGood 1% D Good 5% Good 1% D Good D, P 14 Good Good 1% D Good 2% Good 1% D Good D, P 15 1% D 1% D 1% D Good Good 1 1% D Good small pit Abbreviations and Other Notes for Table 3 "D" means "discoloration"; "SP" means "small pits"; "P" means "pits"; "Good"indicates no pits or discoloration, except sometimes within 0.5 centimeters of the exposed edge, an area which is to be ignored according to the test specifications.
The results in Table 3 suggest that more than 1 ppt of fluorozirconic acid is usually required to achieve excellent corrosion resistance in a single coating, but that even with higher concentrations of fluorozirconic acid, these higher qualityresults are not consistently achieved. (There are at least two apparent possible causes for this inconsistency: slight variations in substrate compositions and unavoidable inconsistencies in the manual application of coating used. Other unrecognizedcauses are also possible, of course.) On the other hand, most of the compositions give excellent results with two coats. This suggests that for touching-up processes, where at least two coats are likely to be used in any event to insure a uniform andfully protective coating, a concentration near 1.0 ppt is likely to be most preferred, because it is more economical than a higher concentration and gives good results if used at least twice. For coating previously unprotected metal, in contrast, if thecoating conditions can be arranged with reliable control, as in conventional continuous processing of coils, for example, and a consistently suitable substrate is used, higher concentrations of fluorozirconic acid would normally be preferred, becausecompositions with such higher concentrations can give excellent corrosion protection in a single coating operation.
In this group, the storage stability of some candidate treatment compositions to be used according to the invention was explored. The compositions were made with the same base solution as for Group 2, with the concentrations of hydrofluoric acidand fluorozirconic acid shown in Table 4. Each composition was placed in a closed container at 49° C. and maintained at that temperature by storage in a thermostatically controlled oven. Each container was examined daily for at least 30 days,unless the formation of a solid precipitate was observed sooner. When precipitate was observed, the storage stability test was ended. Results are shown in Table 4.
TABLE-US-00004 TABLE 4 Concentration in Parts per Thousand of: Days Stored before Any HF H2ZrF.sub.6 Visible Precipitate Formed 0.10 5.0 3 0.25 5.0 13 0.50 5.0 >30 0.75 5.0 >30 1.0 3.0 >30 1.0 5.0 >30 1.0 75 >30 1.0 10 >30
The results in Table 4 indicate that at least 0.50 ppt of HF is required to stabilize a composition that contains at least 5.0 ppt of H2ZrF.sub.6 against formation of a precipitate during storage under practical use conditions.
Field of SearchPhosphorus material
Contains mixture of organic material and at least one inorganic material or elemental component thereof
Liquid reactive coating composition utilized
Contains an atom of hafnium, titanium or zirconium (excludes activating composition)
Contains an atom of chromium
Contains an atom of arsenic, boron or metal atom other than alkali metal
Contains an atom of chromium
Contains an atom or boron, silicon or metal atom other than alkali metal
Metallic compound-containing coating