EP0930379A1 - Verfahren zur Herstellung von Konversionsschichten für niedrigblei Elektrotauchschichten - Google Patents

Verfahren zur Herstellung von Konversionsschichten für niedrigblei Elektrotauchschichten Download PDF

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Publication number
EP0930379A1
EP0930379A1 EP99100326A EP99100326A EP0930379A1 EP 0930379 A1 EP0930379 A1 EP 0930379A1 EP 99100326 A EP99100326 A EP 99100326A EP 99100326 A EP99100326 A EP 99100326A EP 0930379 A1 EP0930379 A1 EP 0930379A1
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Prior art keywords
ions
chemical conversion
liter
electrodeposition coating
lead
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EP99100326A
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English (en)
French (fr)
Inventor
Kenji Tsuge
Satoshi Miyamoto
Shuhei Yamoto
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Nippon Paint Co Ltd
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Nippon Paint Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/20—Pretreatment
    • 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
    • C23C22/07—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 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
    • C23C22/34—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
    • C23C22/36—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 phosphates
    • C23C22/364—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 phosphates containing also manganese cations
    • C23C22/365—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 phosphates containing also manganese cations containing also zinc and nickel cations

Definitions

  • the present invention relates to a method of surface-treating a substrate metal to be subjected to electrodeposition coating. More particularly, the present invention relates to a method of surface-treating a substrate metal for electrodeposition coating on a metal surface by means of an electrodeposition coating bath containing no lead or with low lead content.
  • cationic electrodeposition coating is widely employed as a method for coating a metal of an automobile body and the like.
  • a major cationic electrodeposition coating composition contains an epoxy-resin-based film-forming resin as an amino group containing resin and a blocked polyisocyanate as a cross-linking agent.
  • an anti-corrosion pigment is added to retain the durability of the coating film after the coating treatment.
  • a major anti-corrosion pigment is a lead compound such as a basic lead pigment. Contrary to the fact that this coating composition has an excellent anti-corrosion property, the use of lead is becoming more and more restricted from the view point of its toxicity and, in future, the electrodeposition coating bath should not contain lead.
  • a surface of a metal (hereafter referred to as "substrate metal”) to be subjected to an electrodeposition coating process is pretreated as shown in Fig. 1 with a chemical conversion treatment solution before carrying out the electrodeposition coating process.
  • the chemical conversion treatment solution typically contains zinc, manganese, nickel, fluoride, and the like.
  • Such a chemical conversion treatment solution is prepared on the presupposition that the electrodeposition coating bath contains lead. Therefore, in the case where the electrodeposition coating process is carried out using an electrodeposition coating bath containing no lead or containing lead at less than a predetermined concentration, a sufficient durability of the coating film cannot be obtained by the conventional chemical conversion treatment solution.
  • a purpose of the present invention is to provide a method of pretreatment for a low-lead electrodeposition coating process, which is carried out in an electrodeposition coating bath containing no lead or a low lead.
  • the present invention provides a method of chemical conversion treating a substrate metal useful for a cationic electrodeposition coating process with an electrodeposition coating bath containing a lead at a concentration of not more than 300 ppm, which comprises the step of forming a zinc phosphate film on the metal surface so that a corrosion resistance value according to the AC impedance method is not less than 2,500 ⁇ cm 2 .
  • the present invention concerns a method of chemical conversion treating the substrate metal which is useful for a cationic electrodeposition coating process substantially with zero lead concentration in the electrodeposition coating bath.
  • the present invention concerns a method of chemical conversion treating the substrate metal by subjecting the metal surface to an immersion-treatment with a chemical conversion treatment solution containing 0.5 to 1.5 g of zinc ions, 5 to 30 g of phosphate ions, 0.1 to 4 g of nickel ions, 0.6 to 3 g of manganese ions, 0.05 g or more of fluoride ions, 5 to 20 ppm of copper ions, and a chemical conversion promoter as major components in one liter of the chemical conversion treatment solution.
  • a chemical conversion treatment solution containing 0.5 to 1.5 g of zinc ions, 5 to 30 g of phosphate ions, 0.1 to 4 g of nickel ions, 0.6 to 3 g of manganese ions, 0.05 g or more of fluoride ions, 5 to 20 ppm of copper ions, and a chemical conversion promoter as major components in one liter of the chemical conversion treatment solution.
  • an acidic zinc phosphate film having a corrosion resistance value of not less than 2,500 ⁇ cm 2 according to the AC impedance method can be formed on the surface. Since the film having such a corrosion resistance value is formed, it is possible to form a coating film having an excellent durability even if the electrodeposition coating process is carried out by means of a cationic electrodeposition coating bath with low lead content.
  • the chemical conversion treatment of the present invention provides a method suitable for surface treatment of a metal to be subjected to substrate treatment, prior to cationic electrodeposition coating substantially with no lead content.
  • An electrodeposition coating composition containing no lead for use in the present invention may be, for example, the following composition.
  • a representative low-lead electrodeposition coating composition may be, for example, a cathode electrodeposition coating composition containing components of (A) 40 to 95 wt% of a film-forming resin with an average molecular weight of 500 to 20,000 containing both an amino group and a hydroxyl group and being water-dilutable by acid neutralization and (B) 5 to 60 wt% of a blocked polyisocyanate cross-linking agent.
  • the film-forming resin of the component (A) is a resin with an average molecular weight of 500 to 20,000 containing an amino group (for example, a primary amino group, a secondary amino group, or a tertiary amino group) and a (primary or secondary) hydroxyl group and being water-dilutable with an acid.
  • an amino group for example, a primary amino group, a secondary amino group, or a tertiary amino group
  • a (primary or secondary) hydroxyl group and being water-dilutable with an acid.
  • the amount of amino groups is usually represented by an amino value, which is typically within the range of 30 to 150, preferably within the range of 45 to 80. If the amino value is insufficient, the water-dilution property will decrease.
  • the amount of hydroxyl groups is represented by a primary hydroxyl value, which is typically within the range of 20 to 200, preferably within the range of 50 to 120.
  • the hydroxyl group acts as a cross-linking site.
  • a secondary hydroxyl group, a primary amino group, or a secondary amino group are used as a cross-linking reaction group in addition to a primary hydroxyl group.
  • Such a film-forming resin is typically formed by introducing an amino group to an epoxy resin, an epoxy-containing acrylic copolymer resin, a polyurethane resin, or the like.
  • the blocked isocyanate cross-linking agent (B) is typically obtained by blocking isocyanate groups in a multifunctional isocyanate.
  • the multifunctional isocyanate may be, for example, an aliphatic, alicyclic, and/or aromatic polyisocyanate having two or more isocyanate groups with respect to one molecule.
  • Examples of the multifunctional isocyanate include isomers or isomer mixtures of toluylene diisocyanate, toluylene triisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI), norbornene diisocyanate (NBDI), hexamethylene diisocyanate (HMDI), biphenyl tetraisocyanate, and/or naphthyl tetraisocyanate, and hydrogenated products thereof, such as dicyclohexylmethane diisocyanate.
  • a usable blocking agent is well-known in the art, and examples of the usable blocking agent include aliphatic alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, and cyclohexanol; phenols such as phenol, nitrophenol, cresol, and nonylphenol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, and methyl isobutyl ketoxime; and lactams such as caprolactam.
  • aliphatic alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, and cyclohexanol
  • phenols such as phenol, nitrophenol, cresol, and nonylphenol
  • oximes such as dimethyl ketoxime, methyl ethyl ketoxime, and methyl isobutyl ketoxime
  • lactams such as caprolact
  • Preparation of a cationic electrodeposition coating material composition such as mentioned above can be carried out by blending a metal compound and an optional cross-linking agent to a cationic electrodeposition resin before or after neutralization of the cationic electrodeposition resin and then, after the neutralization if not neutralized yet, conducting a water-dispersion, i.e. an emulsification, or by blending a metal compound and an optional cross-linking agent to an emulsified cationic electrodeposition resin, or by the like method.
  • the neutralization can be carried out by means of a water-soluble organic acid such as formic acid, acetic acid, lactic acid, propionic acid, citric acid, malic acid, tartaric acid, acrylic acid, or sulfamic acid, or an inorganic acid such as hydrochloric acid or phosphoric acid.
  • a water-soluble organic acid such as formic acid, acetic acid, lactic acid, propionic acid, citric acid, malic acid, tartaric acid, acrylic acid, or sulfamic acid
  • an inorganic acid such as hydrochloric acid or phosphoric acid.
  • the cationic electrodeposition coating composition of the present invention may optionally contain ordinary coating material additives, for example, a coloring pigment such as titanium white, carbon black, or red oxide; an extender pigment such as talc, calcium carbonate, mica, clay, or silica; an anti-corrosive pigment, for example a non-pollutant anti-corrosive agent such as zinc phosphate or aluminum phosphomolybdate, and optionally basic lead silicate and the like dispersed in a pigment-grinding resin and used as a paste.
  • an anti-cissing agent, a solvent, a curing catalyst, and the like may be allowed to be contained therein.
  • the cationic electrodeposition coating can be carried out in accordance with a known method, generally by diluting the above-mentioned electrodeposition coating composition with deionized water so that a solid component concentration will be about 5 to 40 wt%, preferably 15 to 25 wt%, adjusting an electrodeposition coating bath, with pH adjusted within the range of 5.5 to 8.0, usually at a bath temperature of 15 to 35°C, and using a substance to be coated as a cathode under the condition of a load voltage of 100 to 450 V.
  • the film thickness of the coating material to be formed by the electrodeposition coating process is not specifically limited, and may be suitably within the range of 5 to 60 ⁇ m, preferably within the range of 10 to 40 ⁇ m, based on the cured coating film. Also, it is suitable that a baking curing temperature of the coating film is generally 100 to 200°C, preferably 160 to 180°C, and the baking is carried out for about 10 to 30 minutes.
  • a zinc phosphate film having a corrosion resistance value of the metal surface of not less than 2,500 ⁇ cm 2 according to the AC impedance method.
  • the inventors of the present invention have found out that, by forming a zinc phosphate film having an AC impedance within this range on the metal surface, a coating film being excellent in durability can be formed by the electrodeposition coating process even if the cationic electrodeposition coating bath does not contain lead ions.
  • the chemical conversion treating method of the present invention is characterized in that an aqueous solution of acidic zinc phosphate containing copper ions is used as a chemical conversion treating agent.
  • the aqueous solution of acidic zinc phosphate according to the present invention contains 0.5 to 1.5 g/liter of zinc ions, 5 to 30 g/liter of phosphate ions, 0.1 to 4 g/liter of nickel ions, 0.6 to 3 g/liter of manganese ions, 0.05 g/liter or more of fluoride ions, 5 to 20 ppm of copper ions, and a chemical conversion promoter as major components.
  • the chemical conversion treatment solution of the present invention contains 0.5 to 1.5 g/liter, preferably 0.7 to 1.2 g/liter, of zinc ions as an essential component. If the zinc ion content is less than 0.5 g/liter, a uniform phosphate film is not formed on an iron-based surface, partially generating a blue-color-like film. On the other hand, if the zinc ion content exceeds 1.5 g/liter, the film on the iron-based surface is likely to be a leaf-like crystal such as generated by a spraying treatment, although a uniform phosphate film is formed, so that it is not suitable as a substrate for cationic electrodeposition coating.
  • the concentration unit g/liter means that the component is contained in gram units per one liter of the chemical conversion treatment solution. Hereafter, the concentration unit g/liter is used in the same sense throughout the specification.
  • the phosphate ions are contained at 5 to 30 g/liter, preferably 10 to 20 g/liter. If the phosphate ion content is less than 5 g/liter, a non-uniform film is likely to be formed. If the phosphate ion content exceeds 30 g/liter, it is not possible to expect an effect that exceeds that of the present invention, and the amount of drugs to be used increases, so that it is economically disadvantageous.
  • the nickel ions are contained at 0.1 to 4 g/liter, preferably 0.3 to 2 g/liter.
  • Nickel ions in the presence of manganese ions further improve the formation film performance, and improve the close adhesion and the anti-corrosion property after the cationic electrodeposition coating process. If the nickel ion content is less than 0.1 g/liter, the effect of adding the nickel ions does not appear. On the other hand, if the nickel ion content is more than 4 g/liter, the amount of the zinc phosphate film decreases, causing adverse effects on the anti-corrosion property.
  • the manganese ions are contained at 0.6 to 3 g/liter, preferably 0.8 to 2 g/liter. If the manganese ion content is less than 0.6 g/liter, the manganese content in the coating film generated on a zinc-based surface decreases, so that the close adhesion between the substrate and the coating film after the cation electrodeposition coating process will be insufficient. If the manganese ion content exceeds 3 g/liter, it is not possible to expect an effect that exceeds that of the present invention, so that it is economically disadvantageous.
  • the fluoride ions are contained at not less than 0.05 g/liter, preferably 0.1 to 2 g/liter. If the fluoride ion content is less than 0.05 g/liter, it is not possible to achieve miniaturization of the crystal of the phosphate film, improvement of the anti-corrosion property after the coating process, and a low-temperature formation process. In the meantime, even if the fluoride ions are allowed to be present in an excessive amount, it is not possible to expect an effect that exceeds that of the present invention, so that it is economically disadvantageous.
  • the fluoride ions are preferably used as complex fluoride ions.
  • the copper ions are contained at 5 to 20 ppm, preferably 10 to 15 ppm. If the copper ion content is less than 5 ppm, the close adhesion of the coating film and the adhesion durability of the coating film are insufficient. On the other hand, if the copper ion content exceeds 20 ppm, the outer appearance changes, so that it is not preferable.
  • zinc oxide, zinc carbonate, zinc nitrate or the like as a source for zinc ions
  • phosphoric acid, zinc phosphate, manganese phosphate or the like as a source for phosphate ions
  • nickel carbonate, nickel nitrate, nickel chloride, nickel phosphate or the like as a source for nickel ions
  • manganese carbonate, manganese nitrate, manganese chloride, manganese phosphate or the like as a source for manganese ions
  • hydrofluoric acid, borohydrofluoric acid, silicohydrofluoric acid, a metal salt thereof for example, zinc salt, nickel salt excluding a sodium salt since it does not produce a desired effect
  • a complex fluoride which is a borofluoride and/or a silicofluoride, or the like can be used as a source for the complex fluoride ions.
  • the chemical conversion promoter may be, for example, sodium nitrite, ammon nitrite, sodium m-benzenesulfonate, hydrogen peroxide, hydroxylamine or the like.
  • the treatment solution of the present invention may further contain nitrate ions and/or chlorate ions.
  • the nitrate ions are preferably contained at a concentration of 1 to 10 g/liter, preferably 2 to 8 g/liter.
  • the chlorate ions are contained at a concentration of 0.05 to 2 g/liter, preferably 0.2 to 1.5 g/liter.
  • As a source for nitrate ions it is possible to use sodium nitrate, ammon nitrate, zinc nitrate, manganese nitrate, nickel nitrate, or the like.
  • As a source for chlorate ions it is possible to use sodium chlorate, ammonium chlorate, or the like.
  • a treatment temperature by means of the chemical conversion treatment solution according to the present invention may be, for example, 30 to 70°C, preferably 35 to 50°C. If the temperature is too low, the chemical conversion property will be poor, requiring a long period of time for the treatment. If the temperature is too high, the balance of the treatment solution is likely to be destroyed due to decomposition of the chemical conversion promoter, precipitate generation of the treatment solution, or the like, so that it is difficult to obtain a good film.
  • the period of time for immersion may be not less than 15 seconds, preferably 30 to 120 seconds. If the period of time for immersion is too short, a film having a desired crystal cannot be sufficiently formed.
  • an immersion treatment may include dipping treatment which may be carried out for not less than 15 seconds, preferably 30 to 90 seconds, and then a spraying treatment is carried out for not less than 2 seconds, preferably 5 to 45 seconds.
  • the spraying treatment is carried out for as long a period of time as possible. Therefore, the immersion treatment according to the present invention includes an embodiment of such dipping treatment / spraying treatment.
  • the present invention also relates to a concentrated treatment agent that provides a treatment solution having the above-mentioned construction. It is sufficient that this concentrated treatment solution contains a source for supplying zinc ions, a source for supplying phosphate ions, a source for supplying nickel ions, a source for supplying manganese ions, a source for supplying fluoride ions, and a source for supplying copper ions at amounts that are sufficient to construct the treatment solution having the above composition by diluting the treatment solution to 1 to 4 weight/volume %.
  • a sodium-based compound must not be contained.
  • the AC impedance of the chemical conversion treated metal surface can be measured as follows on the basis of a principle described in "Basic Electrochemistry” by Shinobu Sotojima [p. 373, published by Asakura Shoten Co., Ltd., July 10, 1967] and "Electrochemistry Measurement Method” by Akira Fujishima, Masuo Aizawa, and Tooru Inoue [pp. 219-222, published by Gihodo Shuppan Co., Ltd., November 15, 1984].
  • a metal plate to be measured was placed in a cell filled with a corrosive solution, and an impedance was measured by sweeping a frequency to calculate a corrosion resistance value by an equivalent circuit analysis shown in Fig. 2.
  • a standard phosphate chemical conversion treatment solution refers to a solution containing the following components in one liter of the treatment solution.
  • Zinc ions 1.0 g/liter Phosphate ions 15.0 g/liter Nickel ions 1.0 g/liter Manganese ions 0.6 g/liter Nitrate ions 6.0 g/liter Nitrite ions 0.14 g/liter Silicon fluoride ions 1.0 g/liter Total acid 21.0 points Free acid 0.7 point
  • the metal plate which had been chemical conversion treated was further washed with water, washed with purified water, and dried, as shown in Fig. 1, to obtain a chemical conversion treated metal plate.
  • a metal plate was immersed in a mixture of alkaline degreasing agents A and B "Surfcleaner SD 250" (manufactured by Nippon Paint Co., Ltd.) (concentration in water is adjusted so that A is contained at 1.5 wt% and B at 0.7 wt%) at 42°C for two minutes.
  • a tap water is used to wash the metal plate at room temperature for 15 seconds.
  • the metal plate is subjected to immersion treatment at room temperature for 15 seconds in a surface-adjusting agent "Surffine 5N-10" (manufactured by Nippon Paint Co., Ltd., at a concentration of 0.1 wt%).
  • a tap water is used to wash the metal plate at room temperature for 15 seconds.
  • Ion-exchanged water is used for immersion treatment of the metal plate at room temperature for 15 seconds.
  • the metal plate is dried for 10 minutes by hot wind of 100°C.
  • the AC impedance of the chemical conversion treated metal plate was measured by the above-mentioned method.
  • a flask equipped with a stirring rod, a cooler, a nitrogen-introducing tube, a thermometer, and a dropping funnel was prepared.
  • Into this flask were added 92 g of 2,4-/2,6-tolylene diisocyanate (weight ratio 8/2), 95 g of methyl isobutyl ketone, and 0.5 g of dibutyltin dilaurate, and further 21 g of methanol was dropwise added to the mixture with stirring.
  • the reaction was started at room temperature and the temperature was raised to 60°C by generated heat.
  • a flask equipped with a stirring rod, a cooler, a nitrogen-introducing tube, a thermometer, and a dropping funnel was prepared.
  • Into this flask were added 199 g of trimer of hexamethylene diisocyanate (Coronate HX : manufactured by Nippon Polyurethane Co., Ltd.) and 11.3 g of ⁇ -caprolactam.
  • the temperature of the contents in the flask was raised to 80°C to uniformly dissolve the mixture, to which were added 32 g of methyl isobutyl ketone, 0.05 g of dibutyltin ldiaurate, and 0.05 g of 1,8-diazabicyclo(5,4,0)-7-undecene.
  • a flask equipped with a stirring rod, a cooler, a nitrogen-introducing tube, a thermometer, and a dropping funnel was prepared.
  • 222.0 g of isophorone diisocyanate was added 222.0 g of isophorone diisocyanate and, after dilution with 39.1 g of methyl isobutyl ketone, 0.2 g of dibutyltin dilaurate was added.
  • 131.5 g of 2-ethylhexanol was dropwise added from the dropping funnel in two hours while the mixture is being stirred by bubbling nitrogen. By suitably cooling the mixture, the temperature was maintained at 50°C during the reaction.
  • 2-ethylhexanol half-blocked isophorone diisocyanate was obtained (with solid components contained at 90%).
  • a flask equipped with a stirring rod, a cooler, a nitrogen-introducing tube, a thermometer, and a dropping funnel was prepared.
  • Into this flask were added 376.0 g of Epon 828 (epoxy resin manufactured by Shell Chemical Co., Ltd.) and 114.0 g of bisphenol A, and the temperature was raised to 130°C under a nitrogen atmosphere. Then, 0.75 g of dimethylbenzylamine was added to carry out a reaction at an exothermic reaction 170°C for one hour to obtain a bisphenol A-type epoxy resin having an epoxy equivalent of 490 g.
  • Pigment-dispersing resin solid components 50%
  • the base resin (350 g) (solid component) obtained in Synthesis Example 1 and the cross-linking agent (150 g) (solid component) obtained in Synthesis Example 2 were mixed, and ethylene glycol mono-2-ethylhexyl ether was added at 3 % (15 g) with respect to the solid components. Then, glacial acetic acid was added for neutralization so that the neutralization degree was 40.5 %, followed by slow dilution with ion-exchanged water. Then, methyl isobutyl ketone was removed under a reduced pressure so that the solid components occupied 36.0 %.
  • a lead-containing electrodeposition coating material was prepared by adding lead acetate in the above-mentioned lead-free electrodeposition coating bath at 1,000 ppm as lead ions.
  • the above-mentioned surface-treated cold-rolled steel plate was immersed as a cathode in these electrodeposition coating baths and, after the electrodeposition was carried out so that the dried film thickness would be 20 ⁇ m, the coating film was cured at 160°C ⁇ 10 minutes for evaluation of the coating film.
  • the durability of the obtained electrodeposition coated plate was measured by the following two methods
  • CCT cycle corrosion test
  • a cut was made in a longitudinal direction on the test piece and, after immersion in 5% aqueous solution of table salt at 40°C for 240 hours, the cut portion was tape-peeled to evaluate the peeling width.
  • the chemical conversion treatment and the cationic electrodeposition coating were carried out in the same manner as in Example 1 except that the standard phosphate chemical conversion treatment solution was used, without any change, as the chemical conversion treatment solution to evaluate the AC impedance of the chemical conversion treated metal plate and the anti-corrosion property of the electrodeposition coating film.
  • the results are shown in Table 1.
  • the chemical conversion treatment and the cationic electrodeposition coating were carried out in the same manner as in Example 1 except that the standard phosphate chemical conversion treatment solution with nickel ions removed and copper ions added instead at 10 ppm was used as the chemical conversion treatment solution to evaluate the AC impedance of the chemical conversion treated metal plate and the anti-corrosion property of the electrodeposition coating film.
  • the results are shown in Table 1.
  • the chemical conversion treated metal obtained according to the method of the present invention has a film having a high corrosion resistance value on its surface.
  • the metal plate having the film with this corrosion resistance value it is possible to form a coating film having an excellent anti-corrosion property even if the cationic electrodeposition coating process is carried out in an electrodeposition coating bath containing no lead or with a low lead content.
  • a chrome rinsing process generally conducted at the last stage of the chemical conversion treatment process is no longer necessary, thereby further reducing the use of a heavy metal.
EP99100326A 1998-01-14 1999-01-12 Verfahren zur Herstellung von Konversionsschichten für niedrigblei Elektrotauchschichten Withdrawn EP0930379A1 (de)

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JP557698 1998-01-14
JP557698 1998-01-14
JP34538898 1998-12-04
JP10345388A JPH11264076A (ja) 1998-01-14 1998-12-04 低鉛ｅｄ用の下地化成処理方法

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Cited By (2)

* Cited by examiner, † Cited by third party
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WO2010071753A1 (en) * 2008-12-18 2010-06-24 Ppg Industries Ohio, Inc. Methods for passivating a metal substrate and related coated metal substrates
US11359288B2 (en) 2016-12-28 2022-06-14 Nihon Parkerizing Co., Ltd. Chemical conversion treatment agent, method for producing chemical conversion coating, metal material having chemical conversion coating, and painted metal material

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WO2010071753A1 (en) * 2008-12-18 2010-06-24 Ppg Industries Ohio, Inc. Methods for passivating a metal substrate and related coated metal substrates
CN102282292A (zh) * 2008-12-18 2011-12-14 Ppg工业俄亥俄公司 使金属基材钝化的方法和相关的涂覆的金属基材
US8282801B2 (en) 2008-12-18 2012-10-09 Ppg Industries Ohio, Inc. Methods for passivating a metal substrate and related coated metal substrates
US11359288B2 (en) 2016-12-28 2022-06-14 Nihon Parkerizing Co., Ltd. Chemical conversion treatment agent, method for producing chemical conversion coating, metal material having chemical conversion coating, and painted metal material

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