PRECOAT CONDITIONING TREATMENT FOR AUTODEPOSITION

Abstract: Blemish and blister formation during autodeposition coating of non-ferrous metal surfaces, particularly galvanized steel and similar zinciferous surfaces, can be greatly reduced by exposing the surfaces to a blemish inhibiting aqueous solution of phosphonates, preferably from an aminophosphonic acid, before autodeposition coating.

Description: Description PRECOAT CONDITIONING TREATMENT FOR AUTODEPOSITION FIELD OF THE INVENTION This invention relates to the use of liquid, usually aqueous, solutions or disper¬ sions in which active metal surfaces of inserted objects are coated with an adherent poly¬ mer film that increases in thickness the longer the metal object remains in the bath, even though the liquid is stable for a long time against spontaneous precipitation or floccula- tion of any solid polymer, in the absence of contact with active metal, i.e., metal that spontaneously begins to dissolve at a substantial rate when introduced into the liquid so¬ lution or dispersion. Such compositions, and processes of forming a coating on a metal surface using such compositions, are commonly denoted in the art, and in this specifica- tion, as "autodeposition" or "autodepositing" compositions, dispersions, emulsions, sus¬ pensions, baths, solutions, processes, methods, or a like term. Autodeposition is often contrasted with electrodeposition, which can produce very similar adherent films but re¬ quires that metal or other objects to be coated be connected to a source of direct current electricity for coating to occur. No such external electric current is used in autodeposi- tion. Autodeposition compositions previously known in the art are effective for coating many metals of practical interest, but it has been observed that attempting autodeposition coating of most zinc-rich metal surfaces such as galvanized steel often results in coatings with many small "pinholes" or larger blisters. Such coatings are usually regarded as aes- thetically unpleasing and often fail to provide the protection against the environment that is normally wanted from autodeposition coatings. Reducing or eliminating the formation of pinholes or larger blemishes in autodeposited coatings, particularly on zinciferous sur¬ faces, more particularly galvanized steel or some variation thereof, is a major object of this invention. DESCRIPTION OF RELATED ART Autodeposition has been in commercial use on steel for about thirty years and is now well established for that use. For details, see for example, U. S. Patents 3,592,699 of July 13, 1971 to Steinbrecher et al.; 4,108,817 of Aug. 22, 1978 and 4,178,400 of Dec. 11, 1979, both to Lochel; 4,242,379 of December 30, 1980 and 4,243,704 of Jan. 6, 1981, both to Hall et al.; and 5,342,694 of Aug. 30, 1994 to Ahmed. (The disclosures of all of these immediately above noted U. S. Patents, except to the extent that they may be incon- sistent with any explicit statement herein, are hereby incorporated herein by reference.) However, preparation of coatings free from flaws on more electrochemically active sub¬ strates such as zinc has continued to prove challenging, especially when using an often preferred chemical type of autodeposition resin, an internally stabilized crystalline copol¬ ymer of vinylidene chloride. DESCRIPTION OF THE INVENTION General Principles of Description Except in the claims and the operating examples, or where otherwise expressly indicated, all 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, however. Also, unless expressly stated to the contrary: per¬ cent, "parts of, and ratio values are by weight; the term "polymer" includes "oligomeΛ", "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 or more 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, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; specifi¬ cation of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole, and any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, ex¬ cept for avoiding counterions that act adversely to the objects of the invention; and the term "mole" and its variations may be applied to ionic, chemically unstable neutral, or any other chemical species, whether actual or hypothetical, that is specified by the types of atoms present and the number of each type of atom included in the unit defined, as well as to substances with well defined neutral molecules. tions after autodeposition and rinsing, and heating or other processes such as steam treat¬ ment to stabilize the initially formed coating film, are generally the same in an extended process according to this invention as in the prior art. Specific preferred conditions are described in the working examples below. Preferably, a process according to this invention also includes a rinse of the wet, although drained, uncured coating formed in the autodeposition bath with one of the aqueous compositions often known in the art as "reactive rinses", also known simply as "rinses". Particularly preferred reactive rinses are described in U. S. Patent 5,372,853 of Dec. 13, 1994 and in U. S. Application Serial No. 08/316,437 filed Sep. 30, 1994, which, except to the extent that they may be inconsistent with any explicit statement herein, are hereby incorporated herein by reference. Other suitable reaction rinses are described in the following U. S. Patents, the specifications of all of which, except to the extent that they may be inconsistent with any explicit statement herein, are hereby incor¬ porated herein by reference: 5,432,694 of Aug. 30, 1994; 5,428,525 of Sep. 30, 1993; and 5,164,234 of Nov. 17, 1992. Any cleaning of the zinciferous surfaced object that is known to be needed or de¬ sired before autodeposition coating in the prior autodeposition art may advantageously be, and preferably is, utilized in connection with this invention before the blemish inhib¬ iting precoating treatment instead. Under certain conditions, it may be advantageous to rinse with water a substrate surface treated with a BIPTC according to the invention before introducing the substrate into the autodeposition bath. Such rinsing is often unnecessary, however, and if not needed is preferably avoided for economy. Characteristic component (A) of a composition according to this invention prefer- ably is selected from the group consisting of phosphonate ions that contain at least one amino nitrogen atom, preferably a tertiary amino nitrogen atom, per ion. Independently, the ions of this characteristic component (A) are preferably selected from ioms that con¬ tain at least 2, or more preferably at least three, phosphonate moieties per ion. Also in¬ dependently, when amino nitrogen is present, divalent hydrocarbon moieties selected from the group of methylene and polymethylene moieties preferably connect the phos¬ phorus atoms in each phosphonate moiety with an amino nitrogen atom; most preferably, these connecting moieties are methylene, with oligomers of methylene increasingly less Summary of the Invention It has now been found that contact of metal surfaces, particularly of galvanized steel or like zinciferous surfaces and of aluminum and its alloys that contain at least 45 % of aluminum, after any cleaning needed or desired but before autodeposition, with an aqueous solution having a surface tension value at 30° C not greater than 55 dynes per centimeter and consisting essentially of, or preferably consisting of, water and: (A) at least 0.008 %, based on the total solution, of a component of dissolved phos¬ phonates, and, optionally, one or both of the following components: (B) a component of dissolved surfactant, exclusive of phosphonates; and (C) a component of dissolved non-oxidizing mineral acid, exclusive of any material that is part of component (A) or (B), is exceptionally effective in reducing formation of pinholes or similar surface blemishes after subsequent autodeposition. For purposes of this description, a "non-oxidizing min¬ eral acid" is defined as in column 2 line 50 - 56 of U. S. Patent 4,477,390 of Oct. 16,1984 to Ledent et al., the entire specification of which, except to the extent contrary to any ex¬ plicit statement herein, is hereby incorporated herein by reference. Such metal pretreat- ment compositions constitute one embodiment of this invention. Another composition embodiment of the invention is a concentrate from which a working composition accord¬ ing to the invention can be prepared by dilution with water. In its simplest embodiment, a process according to this invention comprises three steps: (i) contacting a metal surfaced object with a blemish inhibiting aqueous liquid pre- coating composition as described above at a suitable temperature for a sufficient time to result in fewer blemishes in a subsequently autodeposited coating, this step being denoted briefly as "blemish inhibiting precoating treatment" or "BIPT" and the aqueous liquid composition used being usually briefly denoted hereinafter as "BIPTC"; (ii) removing the metal surfaced object from contact with the BIPTC; and (iii) applying an autodeposit¬ ed coating on the surface treated with the BIPTC in step (i). Detailed Description of Preferred Embodiments The autodeposition composition and process themselves and treatments with oth- er compositions before the BIPT and after autodeposition, for example, cleaning the sub¬ strate before contact with the BIPTC, simple and/or reactive rinses after autodeposition, the use of chromium containing or other known advantageous posttreatment composi- preferred as the number of carbon atoms in these oligomers increases. For convenience and economy, the ions of component (A) are preferably added to the BIPTC in the form of the commercially available corresponding phosphonic acids. The single most preferred source for characteristic component (A) is diethylene triamine- penta{methylene phosphonic acid} with the chemical formula: H 2 PO 3 CH 2 N{(CH 2 ) 2 N-(CH 2 PO 3 H 2 ) 2 } 2 and the second most preferred is aminotri{ methyl¬ ene phosphonic acid} with the chemical formula: N-(CH 2 PO 3 H 2 ) 3 The concentration of characteristic component (A) in the BIPTC can generally vary over a wide range without affecting the effectiveness of blemish inhibition very strongly, particularly with the most effective inhibitors. For each particular molecular type in component (A), there is expected to be a "threshold" value below which little or no inhibition will be achieved. In many cases, there is also expected to be a value, usual¬ ly at least two orders of magnitude above the threshold value, above which the blemish inhibiting effectiveness of a particular molecular type decreases, perhaps because the acidity becomes too high. Therefore, the technically preferable values of concentration of component (A) will depend in detail on the particular molecules used. In addition, the practically preferable value will depend on economics: If the rinse solution is not recycl¬ ed, as is usually more convenient, it is preferable from the cost point of view to use as little of the inhibiting additive as will be adequately effective for the purpose. Generally, from the viewpoint of obtaining maximum inhibition of blemishes, the concentration of component (A) in a working precoat treatment composition according to the invention preferably is, with increasing preference in the order given, at least 0.0085, 0.0088, 0.0091, 0.0094, 0.0097, or 0.0100, %, and for less preferable molecular types more preferably is, with increasing preference in the order given, at least 0.020, 0.030, 0.040, or 0.080 %. Independently, for economic reasons, the concentration of component (A) in a working precoat treatment composition according to the invention preferably is, with increasing preference in the order given, not more than 50, 25, 10, 5, 3, 2, 1, 0.5, 0.3, 0.2, 0.10, 0.080, 0.060, or 0.050 % and for the most preferred molecules for component (A) more preferably is, with increasing preference in the order given, not more than 0.040, 0.020, or 0.015 %. The concentration of phosphonate was determined by titration of a 250 milliliter (hereinafter usually abbreviated "mL") sample of working composition with 0.025 N thorium nitrate solution, after acidification of the sample with a solution of 1 % nitric acid in water to the extent necessary to make the sample clear and light yellow in color and then addition of 1 mL of a solution of 9.45 grams of monochloroacetic acid in a mixture of 40 mL of 5 % NaOH solution in water and 60 mL of additional deionized water, using alizarin indicator, to the first salmon pink end point that persists for at least 30 seconds. Each mL of the titrant solution consumed corresponds to 12.8 part per million of phosphonates in the working composition. In general, the preferred phosphonic acid sources of component (A) are commer¬ cially available only in solution in combination with non-oxidizing mineral acids that act to stabilize the acids against crystallization, as described in U. S. Patent 4,477,390 al¬ ready cited above. Accordingly, compositions according to the invention normally pref¬ erably contain optional component (C). The amount of component (C), when it is made up of hydrochloric acid as is generally most preferred, preferably is such that the ratio of component (C) to component (A), the latter measured as its stoichiometric equivalent of corresponding phosphonic acids, is at least, with increasing preference in the order given, 0.10. 0.15, 0.20, 0.25, 0.28, 0.30, or 0.32:1.0 and independently preferably is not more than, with increasing preference in the order given, 1.0:1.0, 0.80: 1.0, 0.70:1.0, 0.65:1.0, 0.60:1.0, 0.55:1.0, 0.50: 1.0, 0.45: 1.0, 0.40:1.0, 0.37: 1.0, 0.35:1.0, or 0.33:1.0. In order to maximize the probability for avoiding blemishes, the surface tension of the precoat treatment composition according to this invention preferably is, with in¬ creasing preference in the order given, not more than 50, 48, 46, 44, 42, 41, 40, 39, 38, 37, 36, 35, or 34 dynes per centimeter when measured at 30 °C by the Whilmey slide (or plate) method. For details of the measurement of surface tension, see A. Adamson, Phys¬ ical Chemistry of Surfaces, 3rd Ed., (John Wiley & Sons, New York, 1976), p. 23 - 25 and C. Weser, "Measurement of Interfacial Tension and Surface Tension - General Re¬ view for Practical Man", GIT ' Fachzeitschrift fur das Laboratorium, 24 (G-I-T Verlag Ernst Giebeler, Darmstadt, Germany, 1980), 642 - 648 and 734 - 742. Component (A) generally has a slight surface tension reducing effect on other¬ wise pure water, but in order to achieve more preferable values of surface tension for a working precoat treatment composition according to the invention, additional surfactant is generally preferred as a component of the BIPTC. Any surfactant that is (i) chemically stable in combination with component (A) and water, (ii) is effective in reducing the sur- face tension, and (iii) does not have any adverse effect on the quality of the coating sub¬ sequently formed by autodeposition may be used. One group of surfactants that have been found particularly suitable and are effective in economically small concentrations are aromatic sulfonates and their salts, particularly the disulfonated derivatives of dodec- yl diphenyl ether commercially supplied by Dow Chemical Co., Midland, Michigan un¬ der the names DOWFAX™ 2A1 and 2A0 Solution Surfactants. The preferred amounts of any surfactants are those required to attain the preferred surface tension values stated in detail herein. For DOWFAX™ 2A1, which is normally most preferred, the concentra¬ tion in a working BIPTC preferably is, with increasing preference in the order given, at least 0.0003, 0.0006, 0.0009, 0.0012, 0.0015, 0.0018, 0.0021, 0.0024, 0.0027, 0.0030, 0.0032, or 0.0034 % and, primarily for reasons of economy, independently preferably is, with increasing preference in the order given, not greater than 0.05, 0.03, 0.010, 0.0070, 0.0050, or 0.0040 %. The time of contact between the metal substrate being treated and the BIPTC ac- cording to this invention and the temperature during this contact may vary within wide limits. Generally, with the preferred treatment compositions, the contact time preferably is, with increasing preference in the order given, at least 5, 10, 15, 25, 35, 45, 50, 55, or 60 seconds (hereinafter usually abbreviated "sec") and independently, primarily for rea¬ sons of economy, preferably is, with increasing preference in the order given, not more than 30, 15, 10, 5, 4, 3, 2, 1.7, 1.5, 1.3, or 1.1 minutes (hereinafter usually abbreviated "min"). The treatment compositions according to the invention generally are adequately effective at normal ambient temperatures of 20 - 25 ° C and for convenience and econo¬ my are generally preferably used within such a temperature range, although they may be used at any temperature between their freezing and boiling points. The autodeposition bath used for a process according to this invention preferably comprises, more preferably consists essentially of, or still more preferably consists of water and: (A') from 5 to 550, more preferably from 30 to 300, still more preferably from 40 to 120, and most preferably from 40 to 80, g/L of a stably dispersed organic coating resin; (B 1 ) from about 0.4 to about 5, more preferably from 0.5 to 4.0, still more preferably from 1.0 to 3.0, g/L of fluoride ions; (C) an amount sufficient to provide from about 0.010 to about 0.20, more preferably from 0.011 to 0.09, still more preferably from 0.012 to 0.045, oxidizing equival¬ ents per liter of an oxidizing agent selected from the group consisting of dichrom- ate, hydrogen peroxide, ferric ions, and mixtures thereof; and (D 1 ) a source of hydrogen ions in an amount sufficient to impart to the autodeposition composition a pH in the range from 1.6 to 3.8, more preferably from 1.7 to 3.0, still more preferably from 1.8 to 2.5. One preferred type of coating resin for use in forming autodeposited coatings in a process according to the present invention comprises internally stabilized vinylidene chloride copolymers or externally stabilized vinylidene chloride copolymers containing in excess of 50 %, or more preferably at least 80 %, of residues from polymerizing vi¬ nylidene chloride. Most preferably, the vinylidene chloride copolymer is crystalline in nature. Exemplary crystalline resins are described in U.S. Patents 3,922,451 and 3,617, 368, the disclosures of which, except for any part that may be inconsistent with any ex- plicit statement herein, are hereby incorporated herein by reference. Generally, crystal¬ line poly( vinylidene chloride) containing resins comprise a relatively high proportion of residues from vinylidene chloride, for example, at least about 80 % by weight thereof. A second preferred type of resin for use in autodeposition coating in connection with this invention is an acrylic type, particularly copolymers of acrylonitrile. Further details are given in U. S. Patent 4,313,861 of Feb. 2, 1982 to Bassett et al., the disclosure of which, except for any part that may be inconsistent with any explicit statement herein, is hereby incorporated herein by reference. The working BIPTC's may be conveniently prepared on site where used by dilut¬ ing concentrates with water, and such concentrates are also within the scope of this in- vention. Concentrates normally preferably contain from 3 to 20 times the concentrations of components (A), (B), and (C) as described above for working compositions. The practice of the invention, especially in its preferred embodiments, may be further appreciated from the following non-limiting examples and comparison examples. Group 1 General Experimental Procedure The process sequence used for this group of examples is shown in Table 1-1 be¬ low. (Note: All products identified herein by the trademarks PARCO®, RIDOLINE®, Table 1-1 PROCESSING STEPS USED, GROUP 1 General Notes for Table 1-1 "PCL" is an abbreviation for "PARCO® Cleaner". PCL 1530A, with or without added PCL 1530S (see footnote 1 below), is a conventional moderately strong alkaline cleaner with surfactants. Footnotes for Table 1-1 'If substrates were not free from water breaks when using PARCO® Cleaner 1530A alone, 2 g/L of PARCO® Cleaner 1530S were also dissolved in the spray precleaning and dip cleaning fluids. 2 No PCL 1530A or S was deliberately added to this fluid, but because of drag-out from the preced¬ ing stage, it may have contained as much as 10 g/L. 3 The immersion time, along with the solids concentration of the autodepositing composition (within the 6 - 7 % range specified), was adjusted to produce a dry autodeposited coating thickness of 17.8 ± 2.5 micrometers. The solute in this solution is believed to consist predominantly of cobalt fluozirconate after mixing and evolution of gas, presumably carbon dioxide, which occurs after mixing. The solution was replaced after every 100 panels processed. and AUTOPHORETIC®, together with detailed directions for using them as described below, are commercially available from the Parker Amchem Div. of Henkel Corp., Madi¬ son Heights, Michigan.) The precoat treatment bath compositions are shown in Table 1-2 below. Preparation of 18.5 liters (hereinafter usually abbreviated "L") of a "normal acti¬ vation" autodeposition bath was accomplished as follows: Into an adequate size high density polyethylene (hereinafter usually abbreviated as " HDPE") container for the final mixture were added 3.37 kilograms (hereinafter usually abbreviated "kg") of AUTO¬ PHORETIC® 866 Replenisher (hereinafter usually abbreviated "866 Replenisher" or simply "866"), which contains 37.5 % solids, and 12.1 kg of industrially deionized (here¬ inafter usually abbreviated "DI") water. To this first mixture, a separately mixed solution of 0.99 kg of AUTOPHORETIC® Starter 300 (hereinafter usually abbreviated as "Starter 300" or "S 300") and 2.96 kg of DI water was then slowly added with constant stirring, using a motor driven stirrer. Addition of the starter solution to the solution of 866 took approximately 20 minutes. Sufficient hydrofluoric acid was then added to result in a reading of 248 microamperes (hereinafter usually abbreviated "μA") on a LINE- GUARD® 101 fluoride activity meter (hereinafter usually abbreviated "101 Meter"). This composition had an oxidation-reduction potential (hereinafter usually abbreviated "ORP") value for a smooth platinum electrode immersed in the composition, compared to a standard hydrogen electrode, of 375 ±25 millivolts (hereinafter usually abbreviated "mv") Preparation of a "low activation" autodeposition bath was performed identically to the "normal activation" bath, except for using the following amounts of materials: 3.37 kg of 866 Replenisher with 9.24 kg of DI water; 0.70 kg of Starter 300 diluted with 3.12 kg of DI water; and a reading of 110 μA on the 101 Meter. The ORP was the same as for the "normal activation" bath. The coating resin in both these examples of autodep¬ osition baths is a crystalline copolymer of vinylidene chloride. During use, autodeposition baths were maintained between 6 - 7 % of total solids by the addition of 866 Replenisher as needed to compensate for the loss of coating resin from the baths, primarily by transfer of the resin into the autodeposited coatings formed during use. AUTOPHORETIC® Oxidizer 24 was added to maintain the ORP range specified above for each bath, and hydrofluoric acid was added to maintain 101 Meter Table 1-2 PRECOAT TREATMENT BATH COMPOSITIONS, GROUP 1 Notes for Table 1-2 Precoat Designation DI and all other Precoat Designations not beginning with the letter "D" are comparison examples, not according to the invention. "Wt'Vol %" means that the volume of the liquid solution in which the DOWFAX™ surfactants are supplied was measured directly; then the volume percent corresponding to this volume in respect to the volume of the entire composition was multiplied by the weight percent of phosphonic acid(s) in the liquid solution to obtain the "Wt » Vol %." readings of 250 ±25 μA in the "normal activation" (hereinafter usually abbreviated as "NA") autodeposition bath and 1 lO± 10 μA in the "low activation" (hereinafter usually abbreviated as "LA") bath. A separate BIPTC was used for each type (i.e., NA or LA) of autodeposition bath. All metal substrates processed were rectangular panels 10.16 x 15.24 centimeters (hereinafter usually abbreviated "cm") in size; these were prepared by bisecting rectangu¬ lar panels 10.16 x 30.48 cm in size supplied by ACT Laboratories, Inc., Hillsdale, Michi¬ gan. Three types of metal were used: Cold Rolled Steel (hereinafter usually abbreviated "CRS"), Code APR 11721, 6.6 millimeters (hereinafter usually abbreviated "mm") thick, clean, unpolished, Batch 30425414 or 31021314; Hot-dipped Galvanized Steel (hereinaf¬ ter usually abbreviated "G60"), Code APR 10260, 8.9 mm thick; and Galvannealed Steel (hereinafter usually abbreviated "A60"), Code APR 16966, 7.6 mm thick, clean, unpol¬ ished, Batch 20622416 or 20315416. Panels were dipped two at a time, using two hooks attached to the same supporting rod, for the process sequence. A total of 18 panels were processed for each BIPTC: six of CRS, six of G60 and six of A60. Physical testing included GM 95 I IP, 20-cycle, scribe/scab, 504-hour salt spray (ASTM Bl 17-90), impact (ASTM 2794-87, except that no evaluation of the pattern of coating removed by the tape was made), and initial adhesion (ASTM D3359-87) testing. Table 1-3 lists observations of the presence of pinholing blistering on the initially oven cured coated panels as well as impact, GM 951 IP, 20-cycle scribe/scab, salt spray and initial adhesion results. Coatings having significant blistering and/or pinholing after oven cure were not tested further. The following conclusions were drawn from the results shown in Table 1-3: The experimental BIPTC's found to give the best overall performance were those containing DEQUEST™ 2060. Concentrations of at least 0.02 % of this material (which contains only about 50 % of its active phosphonic acid ingredient) appeared to give the best overall results under both low and normal activation conditions for the autodeposi¬ tion bath. G60, A60 and CRS panels were all pinhole and blister-free after oven cure. Initial adhesion was not affected by the precoat treatment step when compared to a DI comparison precoat treatment step, but corrosion results after subsequent autodeposition coating were substantially better with a treatment composition according to the invention. Differences in salt spray and scribe/scab performance results between low and normal Table 1-3 STEEL AND ZINC-ALLOY STEEL COATING PROCESS RESULTS, GROUP 1 ...Table continued on next page . ...Table continued on next page ... ...Table continued on next page . NQtg? fς>r Table 1-3 "Comp. A" is a comparison example in which no precoat treatment was used and the rinse after autodeposition was an aqueous solution of ammonium carbonate, but other process steps were the same as for "normal activation" autodeposition according to the invention. "Comp. B" is a comparison example in which the metal substrate was coated with an electrodepos- ited paint (Powercron™ 500) that is generally considered very high in quality, instead of any auto¬ deposited coating. activation baths were not significant. Coatings after DEQUEST™ 2000 containing pretreatment compositions had com¬ parable salt spray and scribe scab performance to those after DEQUEST™ 2060. Howev¬ er, DEQUEST™ 2000 containing precoat treatments were less effective at pinhole pre- vention over galvannealed A60 panels under "normal activation" bath conditions (101 Meter reading = 250 μA), and appeared to require at least twice as high a concentration as with DEQUEST™ 2060 containing compositions to provide the most corrosion resist¬ ance on the more difficult to protect galvannealed substrates. H 3 PO 4 containing conditioning rinses were unable to produce pinhole-free coatings over galvannealed A60 steel at all precoat concentrations and ACC-866 bath activation levels tested. Salt spray and scribe/scab performance results were slightly lower than for the DEQUEST™ aminophosphonic acid containing BIPTC's. HF - H 2 0 2 mixtures were not effective in eliminating pinholes and blisters on gal¬ vannealed steel. Salt spray (ASTM B 117-90) tests resulted in some field blistering and cathodic de- lamination spots on both G60 and A60 panels for all precoat conditioning rinses tried here. Such results are always or almost always observed during this type of testing of samples with zinciferous surfaces, even when these surfaces are protected with coatings known to give excellent corrosion resistance under practical use conditions. However, the precoat conditioning rinses do appear to reduce the severity of the salt spray induced field blistering and delamination, which are much less severe for A60 panels than for G60 pan- els in general. GM 951 IP, 20-cycle scribe/scab data were excellent for all DEQUEST™ amino- phosphonic acid containing BIPTC's and both ACC-866 bath activation levels tried. Typi¬ cal creep widths for all A60 and G60 panels were 1 mm or less in total creep. Total creep widths over CRS were typically 2 mm, comparable to those now achieved with the best prior art autodeposition technology, indicating that autodeposition coatings applied after a BIPT according to the invention are at least as satisfactory as other autodeposition coat¬ ings on CRS and therefore may be used on composite objects containing both CRS and zinc coated surfaces without deterioration of the best performance now achieved by auto- deposition coating of CRS alone. Impact test results were somewhat erratic as is normal for autodeposition coated CRS substrates, but there is no evidence that the aminophosphonic acid containing BIPT significantly affects impact test performance either adversely or positively. Group 2 A major objective of this group of examples was to establish consumption levels of the BIPTC active ingredients during prolonged use. Unless otherwise stated below, op¬ erating conditions were the same as for Group 1. General Conditions of Operation In preparing the autodeposition baths, 0.94 rather than 0.99 kg of AUTOPHORET- IC® Starter 300 and 2.45 kg instead of 2.96 kg of water were used. The 101 Meter fluoride sensing reading was 150 instead of 240 μamps. A BIPTC concentrate was prepared as follows: In an adequate size HDPE jug were mixed 54.00±0.01 g of Dequest 2060, 4.41 ±0.01 g of Dowfax 2A1 and sufficient DI water to produce a total concentrate mass of 3000± 1 g. To prepare a working BIPTC, 150.0±0.1 g of the aforementioned BIPTC concentrate was then diluted to 3000± 1 g with DI water and stirred. 1300±1 g of this solution was added to a narrow stainless steel panel coating tank designed to accommodate the rectangular test panels, which were 10 by 30 cm in size, with minimal solution volume. Phosphonate concentrations in the working BIPTC's were monitored and main- tained at intervals after use of the BIPTC by removing a 250±1 g sample of the BIPTC (while no substrates were being processed) and titrating this sample with a thorium nitrate solution as already described above. The remaining 1050±1 g of the used working BIPTC was then mixed with an amount of the BIPTC concentrate described above that was calculated, based on the results of the titrated sample, to result in a mixture having the original phosphonate concentration of the working BIPTC in a total mass of 1550 ± 1 g of the mixture, and sufficient DI water to bring the total mass of this mixture to 1550± 1 g was then added and well mixed. A second 250± 1 g sample was then taken from this mixture and titrated as described above, to determine whether the concentration of phos¬ phonate in the mixture had been restored to at least the value originally present in the freshly made BIPTC. If it had, the remaining 1300±1 g of the mixture was usually con¬ tinued in use as replenished used BIPTC to pretreat more substrate panels, as noted in spe- cific instances below. The general process sequence used for this group is shown in Table 2-1 below. The substrate materials used, with the abbreviations for them used in the following de¬ scription shown within quotation marks in parenthesis after each substrate type name be¬ low, were as follows: Cold Rolled Steel ("CRS"), Code APR 11721, 6.6 mm thick, clean, unpolished, Batch . 31216414. Hot-dipped Galvanized ("G60"), Code APR 10260, 8.9 mm thick, clean, unpolished, Batch 20109516. Galvannealed ("A60"), Code APR 16966, 7.6 mm thick, clean, unpolished, Batch 31004416. Hot-dipped Galvanized Cold Rolled Steel, Bimetallic, end-to-end lap joint ("G60/CRS"), Code 10270, Batch 21214416, Panel A: ACTCRS, Panel B: ACT G60. Galvannealed/Cold Rolled Steel, Bimetallic, end-to-end lap joint ("A60/CRS"), Code 10270, Batch 21214416, Panel A: ACTCRS, Panel B: ACT A60. Cured coating appearance data as a function of substrate and use or non-use of the acid cleaning and subsequent rinse steps are shown in Table 2-2 below. "Comparison I" in this table was a commercial product, AUTOPHORETIC® Conditioning Rinse 3180. Panels in this processing sequence were processed one at a time, with the sub¬ strates being processed in the following sequence: First, six each of G60/CRS and A60/ CRS type panels were processed in alternating sequence. Secondly, nine CRS, nine A60 and nine G60 panels were processed, one of each type being processed before a second one of any type was processed, etc. Thirdly, six G60/CRS and six A60/CRS panels were Table 2-1 PROCESSING STEPS USED IN GROUP 2 General Notes for Table 2-1 "RDL" is an abbreviation for "RIDOLINE® Cleaner"; RDL 1007 is a solid, powdered, titanated strongly alkaline cleaner concentrate. "AC 7150" is an abbreviation for AUTOPHORETIC® 7150 Acid Cleaner, a liquid concentrate for preparing a spray cleaning solution designed to remove light rust and oxidation from oil- and grease-free iron and steel surfaces before applying an autodeposition coating. Footnotes for Table 2-1 •This step was used only on substrates that included some cold rolled steel, and not on all such substrates; exceptions are noted in the following tables. 2 The immersion time, along with the solids concentration of the autodepositing composition (within the 6 - 7 % range specified), was adjusted to produce a dry autodeposited coating thickness of 25.4 ± 2.5 micrometers. 3 The solute in this solution is believed to consist predominantly of cobalt fluozirconate after mixing and evolution of gas, presumably carbon dioxide, which occurs after mixing. TABLE 2-2 again processed in alternating sequence. Fourthly, another eleven each of CRS, A60, and G60 panels were processed in the same sequence as before, followed by three each of G60/CRS and A60/CRS panels in alternation with each other. Finally, various control and other test panels were processed as needed. Table 2-3 shows data relevant to the consumption of phosphonate during a process according to the invention. The average consumption calculated from the values in Table 2-3 is 7.6 g of the BITC concentrate per square meter of substrate surface processed. The working BIPTC was analyzed for various elements at the beginning and end of use as described above. Results are shown in Table 2-4. They indicate that zinc is the primary metal dissolved from the substrates during BIPT of galvanized steel according to the invention and that the phosphonate active ingredient is converted to some other sol¬ uble phosphorus containing compound, at least part of which remains in solution in the BIPTC. Physical testing results for Group 2 are shown in Tables 2-5, 2-6, and 2-7 below. TABLE 2-3 The results of Group 2 led to the following conclusions: The D2060/2A1 type BIPTC gave superior coating panel appearance compared to the best previous commercial BIPTC, AUTOPHORETIC® 3180 Conditioning Rinse. Treatment according to the invention described herein gave coatings with no blistering and/or pinholing over CRS and G60 substrate, and only trace pinholing over A60 galvan¬ nealed steel was observed. Elimination of the 7150 acid cleaning step improves coating coverage over a zinc coated steel-to-steel lap joint region with the best example of a BIPT according to the in¬ vention. The initial consumption rate of active ingredient from the BIPTC was calculated to be 39.8 g of phosphonate per 1000 m 2 of substrate processed. Consumption rate dimin¬ ished to approximately 23.7 g of phosphonate per 1000 m 2 between 3.4 and 5.5 m 2 of Abbreviations for Table 2-4 "ppm" = "parts per million"; "m 2 /L" = square meters of substrate per liter of BIPTC. TABLE 2-5 ...Table continued on next page ... Footnotes for Table 2-5 'With the same batch of BIPTC, except for replenishment. 2 The acid cleaning step and immedi¬ ately following rinse step were omitted for this substrate in this instance. Comparison example with AUTOPHORETIC® Conditioning Rinse 3180 rather than a BIPT according to this inven¬ tion. 4 Comparison example with no BIPT other than rinsing with DI water. 'Comparison examp¬ le with no BIPT and with a different reactive rinse, AUTOPHORETIC® Reaction Rinse 2150. Comparison example with electrophoretic paint coating rather than autodeposited coating. substrate processed per liter of starting BIPTC. This may be due to build up of soluble metal phosphonate byproducts in the used BIPTC. A minimum concentration of about 83 ppm of phosphonate in the BIPTC is neces¬ sary for cured coatings to have the best appearance obtained. The nature of the failure or 5 defects depended on the amount of substrate processed through the precoat bath. Lower ...Table continued on next page ... Footnotes for Table 2-6 •With the same batch of BIPTC, except for replenishment. 2 The acid cleaning step and immedi¬ ately following rinse step were omitted for this substrate in this instance. Comparison example with AUTOPHORETIC® Conditioning Rinse 3180 rather than a BIPT according to this inven¬ tion. "Comparison example with no BIPT other than rinsing with DI water. Comparison examp¬ le with no BIPT and with a different reactive rinse, AUTOPHORETIC® Reaction Rinse 2150. 6 Individual results from four replicate samples. Comparison example with electrophoretic paint coating rather than autodeposited coating. concentrations of phosphonate appeared to be adequate to produce cured coating with good appearance as phosphorus containing byproducts built up in the BIPTC. TABLE 2-7 ... Table continued on next page . ... Table conϋnued on next page ... Footnotes for Table 2-7 1 With the same batch of BIPTC, except for replenishment. 2 The acid cleaning step and immedi¬ ately following rinse step were omitted for this substrate in this instance. Comparison example with AUTOPHORETIC® Conditioning Rinse 3180 rather than a BIPT according to this inven¬ tion. Comparison example with no BIP T other than rinsing with DI water. Comparison examp¬ le with no BIPT and with a different reactive rinse, AUTOPHORETIC® Reaction Rinse 2150. Comparison example with electrophoretic paint coating rather than autodeposited coating. Initial adhesion and impact coating test results for coatings over G60 and A60 substrates were unaffected by the amount of substrate processed in the best BIPTC ac¬ cording to the invention, until at least about 3.7 m 2 /L of original BIPTC had been pro¬ cessed. Continued use of replenished used BIPTC after that extent of processing resulted 5 in somewhat lower adhesion and impact test values. Coating performance for coatings over a CRS substrate did not diminish with continued use of replenished used BIPTC. Salt spray tests resulted in some field blistering and cathodic delamination spots for coatings after treatment according to the invention on both G60 and A60 substrates. Variable field blistering was also observed but blister size and/or frequency had no con- 0 sistent trend. All of these results are normal for almost any organic coating over zinc-rich metal surfaces, even for coatings known to give good practical performance. Ratings showed variability with no apparent trend as the area of substrate processed was in¬ creased. Coating performance was slightly better for coatings over the A60 substrate than the G60. Salt spray results over CRS were typically 0-1, comparable to all the types of 5 comparison examples tested, indicating that BIPT according to the invention is not detri- mental to the quality of autodeposited coatings over CRS, which already give fiilly satis¬ factory coating performance. Scribe/scab test results were excellent for coatings after BIPT according to the in¬ vention over G60 and A60 substrates: Typical total creep widths for all A60 and G60 panels were 1 mm or less. Typical creep widths over CRS were 2 mm, closely comparab¬ le to those achieved with currently preferred commercial autodeposition coatings from the same autodeposition compositions as used here.

Claims: CLAIMS 1. A process for forming a protective coating on a solid metallic surface, said process comprising steps of: (I) contacting the solid metallic surface with an aqueous liquid blemish inhibiting pre- coating treatment composition ("BIPTC") having a surface tension value at 30° C not greater than about 55 dynes per centimeter and comprising water and at least about 0.008 % of dissolved phosphonate anions; (II) removing the solid metallic surface from contact with the BIPTC contacted in step (I); and subsequently (HI) autodepositing an organic protective coating on the solid metallic surface from step (II) by contacting the surface with an autodeposition bath. 2. A process according to claim 1, wherein the BIPTC additionally comprises at least about 0.0003 % of a second surfactant in addition to phosphonate anions and has a surface tension not more than about 46 dynes per centimeter. 3. A process according to claim 2, wherein the BIPTC comprises at least about 0.0009 % of surfactant molecules selected from the group consisting of aromatic sulfonates and their salts. 4. A process according to claim 3, wherein the surface tension of the BIPTC is not more than about 40 dynes per centimeter. 5. A process according to claim 4, wherein the BIPTC contains from about 0.0021 to about 0.010 of surfactant molecules selected from the group consisting of dodecyl di- phenyl oxide disulfonic acids and their salts. 6. A process according to claim 5, wherein the ions of component (A) are ions of diethylene triamine pentajmethylene phosphonic acid}. 7. A process according to claim 4, wherein the ions of component (A) are selected from the group consisting of ions of diethylene triamine penta{ methylene phosphonic acid) and ions of aminotri{ methylene phosphonic acid}. 8. A process according to claim 3, wherein the ions of component (A) are selected from the group consisting of ions that (a) contain (a.1) at least one tertiary amino nitrogen atom and (a.2) at least three phosphonate moieties per ion and (b) contain divalent hydro- carbon moieties selected from the group consisting of methylene and polymethylene moieties connecting each phosphorus atom in a phosphonate moiety in the ion to an amino nitrogen atom in the ion. 9. A process according to claim 2, wherein the ions of component (A) are selected from the group consisting of ions that contain at least two phosphonate moieties per ion and in which, if the ions contain an amino nitrogen atom, this atom is bonded to a divalent hydrocarbon moiety that is also bonded to a phosphorus atom in a phosphonate moiety. 10. A process according to claim 1, wherein the ions of component (A) are selected from the group consisting of ions that contain at least two phosphonate moieties per ion. 11. An aqueous liquid composition which either as such or after dilution with additional water is suitable as a blemish inhibiting precoating treatment composition ("BIPTC") before autodeposition, said aqueous liquid composition consisting essentially of water and: (A) at least 0.008 %, based on the total composition, of a component of dissolved phosphonate anions, and, optionally, one or both of the following components: (B) a component of dissolved surfactant, exclusive of phosphonates and their counter¬ ions; and (C) a component of dissolved non-oxidizing mineral acid, exclusive of any material that is part of component (A) or (B). 12. An aqueous liquid composition according to claim 11, wherein said composition includes component (B) to an extent of at least about 0.0003 % and has a surface tension not more than about 46 dynes per centimeter. 13. An aqueous liquid composition according to claim 12, wherein said composition includes at least about 0.0009 % of surfactant molecules selected from the group consist- ing of aromatic sulfonates and their salts. 14. An aqueous liquid composition according to claim 13 having a surface tension that is not more than about 40 dynes per centimeter. 15. An aqueous liquid composition according to claim 14 including from about 0.0021 to about 0.010 % of surfactant molecules selected from the group consisting of dodecyl diphenyl oxide disulfonic acids and their salts. 16. An aqueous liquid composition according to claim 15, wherein the ions of com¬ ponent (A) are ions of diethylene triamine penta{methylene phosphonic acid}. 17. An aqueous liquid composition according to claim 14, wherein the ions of com¬ ponent (A) are selected from the group consisting of ions of diethylene triamine penta{methylene phosphonic acid} and ions of aminotri{ methylene phosphonic acid}. 18. An aqueous liquid composition according to claim 13, wherein the ions of com¬ ponent (A) are selected from the group consisting of ions that (a) contain (a.1) at least one tertiary amino nitrogen atom and (a.2) at least three phosphonate moieties per ion and (b) contain divalent hydrocarbon moieties selected from the group consisting of methylene and polymethylene moieties connecting each phosphorus atom in a phosphonate moiety in the ion to an amino nitrogen atom in the ion. 19. An aqueous liquid composition according to claim 12, wherein the ions of com¬ ponent (A) are selected from the group consisting of ions that contain at least two - phosphonate moieties per ion and in which, if the ions contain an amino nitrogen atom, this atom is bonded to a divalent hydrocarbon moiety that is also bonded to a phosphorus atom in a phosphonate moiety. 20. An aqueous liquid composition according to claim 11, wherein the ions of com¬ ponent (A) are selected from the group consisting of ions that contain at least two phos¬ phonate moieties per ion.

Inventors: CORMIER GERALD J, KLEIN JAMES W, CORMIER, GERALD, J., KLEIN, JAMES, W.
Applicants: CORMIER GERALD J, HENKEL CORP, KLEIN JAMES W, CORMIER, GERALD, J., HENKEL CORPORATION, KLEIN, JAMES, W.
Application year: 1996
Main classification: B05D1
IPC codes: B05D3, B05D7, C23C22