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
  • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
  • C23C22/33—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also phosphates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
  • C23C22/30—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also trivalent chromium
• • 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
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/37—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also hexavalent chromium compounds
• • 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
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/37—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also hexavalent chromium compounds
  • C23C22/38—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also hexavalent chromium compounds containing also phosphates

Definitions

• This invention relates to chromate treatment bath compositions and treat ⁇ ment methods for application to metals. More particularly, the present invention relates to a chromate treatment bath composition that, when dried into place on the surface being treated, can provide metal surfaces with a sparingly soluble chromate film that exhibits an excellent coatability with waterborne paints and at the same time has an excellent corrosion resistance, paint adherence, alkali resistance, and water resistance. The invention also relates to a treatment method using said chromate treatment bath composition. DESCRIPTION OF RELATED ART
• dry-in-place chromate treatment technology is able to form a chromate film on metals simply by coating the metals and then drying.
• a distinguishing feature of dry-in-place chromate treatment is that it is not limited to particular metal substrates.
• dry-in-place chromate treatment is frequently used to impart corrosion resistance to metal surfaces, to improve their adherence to resins, and most importantly to improve paint adherence and post-painting corrosion resistance when painting is carried out.
• the main metals used in flat sheet structures are zinc- iferous-plated steel sheet and aluminum and aluminum alloy flat sheet.
• the corrosion-inhibiting hexavalent chromium is soluble in the water in wet corrosive ambients, and as a result one drawback to dry-in-place chromate films is that they are generally more soluble in water than reactive or electrolytic chromate films
• the main component exhibiting water solubility in dry-in-place chromate films ts the hexavalent chromium ions, and films exhibiting a high water solubility of this type are denoted below as "low-fixed-chromium" films
• the hexavalent chromium ions is a pollutant, and this fact has generally created demand for a sparingly water soluble dry-in-place chromate film having a high proportion of fixed or immobilized chromium
• a very recent trend with flat sheet metal stock is that the stock is increasingly being painted with organic resin at the manufact ⁇ uring stage, in order to obtain various characteristics, such as corrosion resist ⁇ ance, fingerprint resistance, lubricity, and insulating characteristics.
• organic resins solvent-based resins are being replaced by waterborne resins for the same environmental reason as above.
• the hexavalent chromium ions eluted from dry-in-place chromate coatings inhibit dispersion of the waterborne resin in such waterborne resin coatings. This either prevents normal application and formation ofthe resin coating or ends up gelling the resin coating bath itself.
• Dry-in-place chromate treatment baths generally take the form of Cr 3 "- containing aqueous chromic acid or dichromic acid solutions, and several meth ⁇ ods have already been proposed that provide sparingly water soluble dry-in-place chromate films using such baths.
• Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 61-58552 [58,552/1986] discloses a method that uses a chromating bath based on chromic acid, chromic acid reduction product, and silica sol.
• the hexavalent chromium in the chromate film is still readily eluted when surface- treated steel sheet bearing a chromate film formed by this method is submitted, during processing and painting operations, to a pre-paint alkaline rinse. This causes the corrosion resistance of the film to decline.
• Sho 58-22383 [22,383/1983] and Sho 62-83478 [83,478/1987] teach the use of silane coupling agent to reduce hexavalent chromium ions in the chromate treatment bath.
• the coatings afforded by these methods have an excellent paint film adherence.
• the chromate film afforded by the form- er method has a poor alkali resistance, because it is laid down from a phosphoric acid-free chromate treatment bath.
• the chromate film afforded by the latter method also has a similarly inadequate alkali resistance.
• Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 63-96275 [96,275/1988] teaches a treatment method that uses a chromate treatment bath containing organic resin whose molecule has been functionalized with specific amounts of hydroxyl group
• the alkali resistance is again often in ⁇ adequate in this case because the organic resin in the chromate coating formed by this method contains carboxyl moieties produced by oxidation by chromic acid
• the treatment bath stability in this case is strongly impaired because the reaction of the hydroxyl-functional organic resin and chromic acid proceeds even in the treatment bath itself.
• Japanese Patent Publication [Kokoku] Number Hei 7-33583 [33,583/1995] teaches a chromate treatment method that uses a chromate treatment bath containing carboxylic acid and/or a carboxylic acid derivative This chromate treatment bath affords only an inadequate improvement in application performance.
• this method entails substantial cost for its heating facilities, which runs counter to the current trend of economizing on energy.
• drying temperatures not ex ⁇ ceeding 100 °C are desirable in order to fully exploit the overall merits of dry- in-place chromate treatment systems.
• a chromate treatment bath composition for application to metals characteristically comprises, preferably consists essentially of, or more preferably consists of (A) an aqueous chromate solution containing hexavalent chromium ions and trivalent chromium ions, and (B) a nonionic-anionic composite surfactant that has an anionic moiety and a nonionic moiety comprising at least 1 selection from polyethylene glycol groups and groups composed of ethylene oxide addition polymers in which at least 2 ethylene oxide molecules have been added in addition to a hydrophobe moiety
• the weight ratio of nonionic-anionic composite surfactant to hexavalent chromium ions concentration in a composition according to the present invention is from
• a chromate treatment bath composition according to the present invention can, and normally preferably does, also contain phosphate ions and silica, and may also contain other ingredients, such as fluorine-containing anions, soluble salts of metals, e g , zinc, iron, nickel, aluminum, titanium, and zirconium, water-soluble polymers such as polyacrylic acids, maleic acid-methyl vinyl ether copolymers, polyacrylamides, and so forth, and acrylate ester copolymer emulsions, styrene-acrylate ester copolymer emulsions, epoxy resin emulsions, ethylene-acrylic acid copolymer emulsions, and polyester resin emulsions
• the addition of an emulsion of an epoxy resin with a bisphenol skeleton is effective in increasing the paint adherence of the corresponding film.
• a method according to the present invention for chromate treatment of metal surfaces characteristically comprises forming and fixing a chromate film at a chromium add-on of 5 to 150 milligrams per square meter of surface treated, hereinafter usually abbreviated as "mg/m 2 ", measured as chromium metal, on the surface, by coating the surface with a layer of a chromate treatment bath composition according to the present invention and then drying the surface of the metal with this layer in place on the surface.
• mg/m 2 milligrams per square meter of surface treated
• the concentrations of hexavalent chromium ions and trivalent chromium ions in an aqueous inorganic chromate solution according to the invention are not critical.
• the total chromium ions concentration (hexavalent chrom ⁇ ium ions + trivalent chromium ions) is preferably from 1 to 100 grams per liter (hereinafter usually abbreviated as "g/L").
• concentrations below 1 g/L the corrosion resistance of the obtained coating can be unsatisfactory, unless a very thick layer of the bath is used, and controlling the drying of such a thick layer to avoid inconsistencies from one point to another on a treated surface is technical ⁇ ly difficult.
• Concentrations above 100 g/L result in a high chromate bath viscosity and in addition reduce bath stability and thereby substantially hinder control of the chromium add-on to desired values.
• the trivalent chromium ions/hexavalent chromium ions weight ratio is preferably in the range from 0.25 to 3.5.
• the hexavalent chromium content in the resulting film will be too high when this ratio falls below 0.25 and the film can exhibit an unsatisfactory water resistance.
• this ratio exceeds 3.5 the hex ⁇ avalent chromium content in the resulting film will be too low and the film can ex ⁇ hibit an inadequate corrosion resistance.
• the trivalent chromium ions/hexaval- ent chromium ions weight ratio can be controlled and adjusted by the addition of the usual reductants, such as ethanol, methanol, sucrose, and the like.
• Molecules of the characteristic nonionic-anionic composite surfactant used in the present invention have a hydrophilic part and a hydrophobic part
• the hydrophilic part has a composite structure that contains a nonionic moiety and a distinct anionic moiety
• the nonionic moiety has a structure that contains at least one selection from polyethylene glycol groups and groups composed of ethylene oxide addition polymers in which at least two ethylene oxide molecules have been added, or in other words contains a moiety conforming to the general formula -(C 2 H 4 O) n -, where n is a positive integer with a value of at least two Sur ⁇ factants whose molecules contain such a nonionic moiety and a distinct anionic moiety in one hydrophilic group are called "nonionic-anionic composite surfact ⁇ ants" within the context of the present invention
• the surfactant used in the present invention must have the structure de ⁇ scribed above for the composite hydrophilic group, but is not otherwise narrowly restricted, and any single selection or plural number of selections from the above-described nonionic-anionic composite surfactants can be used in the present invention
• the special nonionic moiety in the composite hydrophilic part is bonded to the hydrophobic part through a non-ester linkage
• Nonionic-anionic composite surfactants used by the present invention are exemplified by compounds in which a molecule of a hydrophilic acid with at least two lonizable hydrogen atoms, such as sulfuric acid, phosphoric acid, carbonic acid, and the like, has been bonded to a nonionic surfactant molecule by one or more bonds that replace less than all of the lonizable hydrogen atoms of the hy ⁇ drophilic acid, as illustrated below Salts of such compounds can also be used as the nonionic-anionic composite surfactant
• nonionic surfactant containing a hydrophobic part and a nonionic hydrophilic part that can serve as a precursor for a nonionic-anionic composite surfactant needed in a composition of the pres ⁇ ent invention
• ethylene oxide adducts of i) higher alcohols, (n) fatty acids, (in) fatty acid esters of polyhydric alcohols, (iv) higher alkylamines, (v) fatty acid am- ides, and (vi) polypropylene glycol, (2) ethylene oxide adducts of phenol, alkylphenols, styrenated phenol, and polycyclic aromatic compounds (e g , naphthalene, anthracene, etc ), and (3) ethylene oxide adducts of condensates between (i) an aldehyde (e g , for ⁇ maldehyde or acetaldehyde) or a ketone (e.g., acetone or
• ethylene oxide adducts of higher alcohols and the ethylene oxide adducts of alkylphenols are preferred for their ease of commercial acquisition
• a nonionic-anionic composite surfactant effective in the present invention can be obtained by reacting a hydrophilic acid, e g , sulfuric acid, phosphoric acid, or carbonic acid, with a nomonic hydrophilic group-functionalized surfactant as described above to yield the anionic sulfate ester (-OSO 3 H), sulfonic acid (- SO 3 H), phosphate ester (-OPO 3 H), or carboxylic acid (-COOH) or salt thereof
• a phosphate ions/total chromium ions weight ratio of from 0.1 to 2.0 is preferred, and for pur ⁇ poses of calculating this ratio, the stoichiometric equivalent as orthophosphate ions (i.e, PO 4 '3 ) of all inorganic acids that contain phosphorus in its +5 valence state and all salts thereof added to the composition in the course of preparing it is considered to be present as phosphate ions, irrespective of the actual de ⁇ gree of ionization that may exist in the composition.
• this ratio is below 0.1 , the resulting chromate film tends to have a lower alkali resistance and corrosion resistance than are desirable.
• Silica is also preferably present in a chromate treatment bath composition according to the present invention.
• the effects from silica addition are, for ex ⁇ ample, improvements in the corrosion resistance, paint adherence, and scratch resistance of the resulting chromate film.
• the preferred silica sol content corre- sponds to a silica sol/total chromium ions weight ratio (solids) of from 0.2 to 6.0.
• the effects from addition may be inadequate when this weight ratio is below 0.2. When this ratio exceeds 6.0, the effects from silica addition become saturated and such additions are thus economically undesirable.
• such addi ⁇ tions can cause an unacceptably low water-resistant secondary adherence to a paint film after painting.
• Silica used in the present invention preferably is selected from the group consisting of colloidal silicas, silica sols, and fumed silicas, in each case with a particle size of 5 to 300 nanometres (hereinafter usually abbreviated as "nm"). Irregularities in the film surface may be produced when the film is prepared using a treatment bath that contains silica with a particle size in excess of 300 nm. This can impair the gloss aspect of the appearance. In the case of a coating treatment bath containing silica sol with a particle size below 5 nm, the specific surface of the silica sol becomes so large that bath stability can be impaired
• a chromate treatment bath composition for metals according to the pres ⁇ ent invention also preferably contains fluorine ions or fluoride ions
• the source of said fluorine ions or fluoride ions is not critical, but is preferably hydrofluoric acid or a complex hydrofluoric acid such as fluosilicic acid, fluozirconic acid, or fluotitamc acid
• the fluorine ions/total chromium ions weight ratio is preferably from 0 01 to 1 0 When this weight ratio is below 0 01 , the etching activity may be undesirably weak, so that removal ofthe metal oxides from treated metal sur- faces will be inadequate On the other hand, at values in excess of 1 0, the etching activity becomes so strong that the corrosion resistance of the treated metal is diminished
• the metal substrate on which a chromate treatment according to the in ⁇ vention may be executed is not narrowly restricted, but steel sheet commercially plated with zinc or zinc alloy, aluminum, and/or aluminum alloys is particularly suitable
• the chromium add-on from application of a chromate treatment bath com ⁇ position according to the present invention is also not narrowly restricted, but the preferred range for the chromium add-on on the metal surface is from 5 to 150 mg/m 2 (as chromium metal)
• a chromium add-on below 5 mg/m 2 often causes the resulting chromate film to have an inadequate corrosion resistance
• a chromium add-on in excess of 150 mg/m 2 reduces the improvement in chromium fixing ratio afforded by the present invention
• an excessively thick chromate coating raises the possibility of a deterioration in the physical proper- ties of the film due to, for example, cracking during drying
• the pH of the treat ⁇ ment bath composition according to the present invention is also not particularly critical, but as a general rule is preferably maintained below 3 0
• the method for drying the subject coated chromate layer is also not par ⁇ ticularly critical, and the drying method can be selected from hot air-current dry- ing, high-frequency induction heating, and so forth
• the drying temperature after application of the subject chromate treatment bath composition is again not critical, but metal sheet temperatures in the range from 60 °C to 150 °C are pre ⁇ ferred Sheet temperatures below 60 °C usually cause a diminished productivity due to the long times required for the reaction between the hexavalent chromium and nonionic-anionic composite surfactant High sheet temperatures, in excess of 150 °C, are uneconomical due to the associated increase in equipment costs
• a hydration layer is formed by water molecules around the nomonic moiety of the hydrophilic part of the nonionic-anionic composite surfactant molecules present in a composition according to the invention and that this hydration layer protects against or de- fleets the strong oxidizing activity of the hexavalent chromium ions, which other ⁇ wise would
• the nonionic-anionic composite surfactant also functions to reduce the surface tension of the chromate treatment bath composition according to the present invention
• Chromate treatment generally involves application of the chromate treatment bath composition to metal followed by drying
• a high surface tension chromate treatment bath composition ts applied the variation or unevenness produced during application is directly converted into coating irregu ⁇ larities by drying, this is a problem for the appearance
• a chromate treatment bath composition according to the present invention has a low surface tension and application inhomogeneities are rapidly extinguished after applica- tion to the metal Accordingly, post-drying application irregularities become in ⁇ significant and the coated sheet will have an excellent appearance
• the subject nonionic-anionic composite surfactant also functions to improve the ap ⁇ plication performance of a chromate treatment bath composition according to the present invention If the chromate treatment bath composition according to the present in ⁇ vention exhibits high foaming due to the activity of the surfactant contained therein, the foaming can be reduced by the addition of an antif
• Chromate treatment bath A with the composition given in Table 1 was prepared by the following procedure First, 50 grams (hereinafter usually abbre ⁇ viated as "g") of chromic anhydride was dissolved in 500 g of water Methanol was then added to the aqueous solution to reduce a portion of the chromic acid and give a hexavalent chromium lons/tnvalent chromium ions weight ratio of 7/3 The surfactant was preliminarily dissolved in water to give an aqueous solution that was added to the aqueous solution containing hexavalent chromium ions and trivalent chromium ions, and the result was brought to a total of 1 kg by the addition of water
• the chromate treatment baths B to H and J to N reported in Table 1 were each prepared with the compositions reported in Table 1 , using the same general procedure as for chromate treatment bath A, but with different amounts and types of material where so specified 12) Preparation of the test specimens
• Test specimens were prepared by the following treatment sequence workpiece (note 1 ) - alkaline degreasing (note 2) - water rinse - roll squeegee - drying (air-current drying) ⁇ application of the dry-in-place chromate bath (note 3) - drying (note 4) Notes on the treatment sequence
• the dimensions of the workpiece were 200 x 300 mm with a sheet thickness of 0 6 to 0 8 mm
• alkaline degreasing consisted of treatment at 60 °C by spraying for 30 seconds with a 2 % aqueous solution of PALKLINTM 342 weakly alkaline degreaser
• g/kg means "grams of ingredient per kilogram of total composition
• the SiO 2 used was SNOTEXTM O obtained from Nissan Kagaku Kabushiki Kaisha.
• the Surfactant/Cr 6* ratio is based on active surfactant solids only. . Table I is continued on the next page. .
• alkaline degreasing consisted of treatment at 60 °C by spraying for 2 minutes with a 2 % aqueous solution of FINECLEANERTM 4327 nonetching degreaser (commercially available from Nihon Parkerizing Co., Ltd.).
• the dry-in-place chromate treatment bath was used diluted with water to a total chromium ions concentration (hexavalent chromium ions + trivalent chromium ions) of 13.0 g/L. It was applied using a groove roll at a chrom ⁇ ium add-on (after drying) of 30, 50, or 100 mg/m 2 (controlled by adjusting the downward pressure of the applicator roll).
• Drying consisted of achieving a maximum sheet temperature of 100 °C in a hot air-current oven.
• test specimen treated as described above was sprayed for 2 minutes at 60 °C with a 2 % aqueous solution of PALKLINTM N364S mod- erately alkaline degreaser (commercially available from Nihon Parkerizmg
• test specimen treated as described above was bar coated with DELI- CONTM #700 melamine-alkyd paint (commercially available from Dai Nippon Tor- yo Co., Ltd.) so as to give a paint film thickness of 25 micrometers. This was fol ⁇ lowed by baking at 140 °C for 30 minutes to yield a painted sheet. This painted sheet was submitted to the following paint performance tests.
• C -1 Primary adherence
• a grid of 100 squares (1 mm x 1 mm) was scribed into the painted surface using a knife cutter. The grid region was then extruded 5 mm us ⁇ ing an Erichsen tester and thereafter peeled with cellophane tape. The number of remaining squares was counted for the evaluation.
• test specimens fabricated as above were bar coated with ARON- MELTTM waterborne polyester resin (commercially available from Toa Gosei Ka ⁇ bushiki Kaisha) so as to give a resin film thickness of 1.0 micrometer. This was followed by drying in a hot air-current oven to a maximum attained sheet temper ⁇ ature of 100 °C. The status of the coating was then evaluated on the following scale: excellent + + the waterborne resin was uniformly coated;
• Table 2 below reports the test results from the various performance tests and Table 3 below reports the results of the chemical stability tests of the chro ⁇ mate treatment baths in Table 1.
• Bath compositions J, K, and M used surfactants with chemical structures differing from that according to the present invention, and in each case were un ⁇ stable to the strong oxidizing activity of the hexavalent chromium ions and thus had such poor chemical stabilities that their other performance characteristics could not practically be evaluated.
• Surfactant-free bath composition L (Compara ⁇ tive Examples 1 and 2) did have a good chemical stability, but it gave a resist ⁇ ance to chromium elution that was inferior to that afforded by chromate treatment bath compositions according to the present invention, did not provide good coat ⁇ ability by waterborne resin, and did not provide a satisfactory coating appearance 0 by the chromate treatment bath itself.
• Bath composition N whose surfactant lacked an anionic moiety, had a chemical stability lower than the chromate com ⁇ positions in the examples.
• the invention described above produces an excellent coating appearance, 5 decreases elution of Cr(VI) from the chromate film, provides excellent coating by waterborne resins, is chemically stable, and provides coatings with high quality corrosion resistance either bare or painted.

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• 1995
  • 1995-11-30 JP JP31295195A patent/JPH09157864A/ja active Pending
• 1996
  • 1996-11-27 EP EP96942777A patent/EP0877832A4/de not_active Withdrawn
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