Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/53—Treatment of zinc or alloys based thereon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
  • B05D3/102—Pretreatment of metallic substrates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings

Definitions

• 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.
• 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.
• 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".
• 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.
• 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.
• 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.
• 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.
• 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
• % 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 component of dissolved surfactant, exclusive of phosphonates (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.
• 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.
• 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.
• 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).
• 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
• 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.
• component (A) is 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:
• 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.
• concentration of component (A) can generally vary over a wide range without affecting the effectiveness of blemish inhibition very strongly, particularly with the most effective inhibitors.
• 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 %.
• 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.
• compositions according to the invention normally pref ⁇ erably contain optional component (C).
• 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,
• 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.
• 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.
• 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 DOWFAXTM 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.
• 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 % 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.
• 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
• 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.
• 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.
• 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.
• 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.
• 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”)
• 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 DOWFAXTM 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 ⁇ A in the "normal activation” (hereinafter usually abbreviated as "NA”) autodeposition bath and 1 lO ⁇ 10 ⁇ A 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
• CRS Cold Rolled Steel
• mm 6.6 millimeters
• A60 Galvannealed Steel
• 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
• 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.
• Comp. B is a comparison example in which the metal substrate was coated with an electrodepos- ited paint (PowercronTM 500) that is generally considered very high in quality, instead of any auto ⁇ deposited coating.
• PowercronTM 500 an electrodepos- ited paint
• 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 DEQUESTTM aminophosphonic acid containing BIPTC's.
• 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.
• 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 DEQUESTTM 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.
• 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
• 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
• 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
• 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.
• 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
• 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.
• 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.
• 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
• 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.
• 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.

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  • 1996-08-26 CA CA002230278A patent/CA2230278A1/en not_active Abandoned
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