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EP0224065A1 - Procédé pour obtenir des couches à base de chromate - Google Patents

Procédé pour obtenir des couches à base de chromate Download PDF

Info

Publication number
EP0224065A1
EP0224065A1 EP86115014A EP86115014A EP0224065A1 EP 0224065 A1 EP0224065 A1 EP 0224065A1 EP 86115014 A EP86115014 A EP 86115014A EP 86115014 A EP86115014 A EP 86115014A EP 0224065 A1 EP0224065 A1 EP 0224065A1
Authority
EP
European Patent Office
Prior art keywords
chromium
chromate
ions
chromating
layers
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP86115014A
Other languages
German (de)
English (en)
Other versions
EP0224065B1 (fr
Inventor
Haruyoshi Terada
Akimitsu Fukuda
Yohji Ono
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nihon Parkerizing Co Ltd
Original Assignee
Nihon Parkerizing Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nihon Parkerizing Co Ltd filed Critical Nihon Parkerizing Co Ltd
Priority to AT86115014T priority Critical patent/ATE40158T1/de
Publication of EP0224065A1 publication Critical patent/EP0224065A1/fr
Application granted granted Critical
Publication of EP0224065B1 publication Critical patent/EP0224065B1/fr
Expired legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/38—Chromatising

Definitions

  • the invention relates to a process for the production of chromate layers on surfaces made of zinc or zinc alloys electrochemically by means of chromate-containing aqueous chromating baths.
  • a difficulty in setting the desired layer weight is also that either the concentration of the treatment solution varies or e.g. the shape or the pressure of the application rolls must be changed. These difficulties increase as relatively rapid changes in layer weight become necessary.
  • the object of the invention is to eliminate the shortcomings of the known processes for producing chromate layers, in particular the abovementioned shortcomings, and to provide a process which leads to chromate layers having an excellent appearance and very good properties with regard to corrosion resistance and adhesion promotion for a subsequently applied organic coating .
  • the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the chromate layers are removed using a Chromatierbades generated, the ions 5 to 70 g / 1 Ch rom 6+, 0.01 to 5.0 g / 1 Chrom3 + - ions, 5 to 100 g / 1 of silica and / or silicate and 0.05 to 10 g / 1 contains nitrate ions, the weight ratio of chromium 3+ : chromium 6+ being in the range from 1:50 to 1: 3.
  • the chromium 6 + - can ion-chromic anhydride, ammonium and alkali metal dichromate individually or are incorporated into the mixture in the bath.
  • concentration of the chromium 6+ ions is essential in that in the case of a concentration below 5 g / 1 with continuous treatment of the workpiece to be machined, the speed of the coating formation drops and it becomes difficult at the same time to achieve uniform coating formation. If the concentration is more than 70 g / l, no improvement in the chromate layer formed can be determined. In addition, such high concentrations lead to a strong and undesirably high zinc dissolution. Finally, considerable quantities of treatment bath are discharged from the treated workpiece, which is ultimately uneconomical.
  • the chromium ions can be added to the chromating bath in the form of nitrate or carbonate compounds. It is also possible that chromium 3+ ions by the reduction of chromium + 6 - ion with organic substances, such as alcohol, starch, or tannic acid to introduce. Due to the chromium 3+ content, an increased deposition of chromate layer is achieved with the same amount of electricity.
  • the perfect ratio of chromium 3+ : chromium 6+ is also decisive for the aforementioned effect. If the chrome is 3+ : Chromium 6 + - ratio below 1: 50, the described effect weakens. With a chromium chromium 6 + ratio above 1: 3, the ability of the chromate layer to absorb organic coatings decreases.
  • silica and / or silicate pursues the goal of converting the chromating bath into a dispersion in which the dispersed particles have a size of about 1 to 100 / um. At a concentration below 5 g / 1, the corrosion resistance and paint adhesion decrease. No further improvement can be achieved with concentrations above 100 g / l. In addition, there is a risk that silicic acid and / or silicates separate out and an excessive amount of chromating bath is discharged from the workpiece to be treated.
  • the nitrate ions can be added to the chromating bath in the form of nitric acid, ammonium and alkali nitrate individually or as a mixture.
  • concentration range is important insofar as a perfect layer formation is no longer guaranteed below 0.05 g / l (cf. Comparative Example 3 in Table 3). In particular, corrosion resistance and paint adhesion decrease. At concentrations above 10 g / 1, an additional improvement in the characteristics of the chromate layer formed can no longer be determined. In addition, higher nitrate levels lead to increased zinc dissolution and a reduction in layer weight.
  • the pH of the chromate bath is not critical. However, it is particularly expedient to generate the chromate layers using a chromating bath, the pH of which is in the range from 1 to 6.
  • the pH of the chromate layer does not change at pH values below 1, but there is a risk that the amount of zinc released from the metal surface will increase and the weight of the chromate layer formed will decrease. If the pH is higher than 6, the character of the chromate layer formed is also retained, however, a separation of silica and / or silicate can hardly be avoided.
  • ammonium hydroxide alkali hydroxide or an alkali carbonate.
  • the temperature of the treatment solution is advantageously between room temperature and 70 ° C. Although a higher temperature does not change the character of the chromate layer formed, it should not exceed the limit of 70 ° C for economic reasons.
  • the electrochemical treatment is carried out at a cathodic current density of 3 to 80 A / dm 2 .
  • a current density below 3 A / dm 2 a perfect layer formation is hardly guaranteed. Corrosion resistance and paintability are also becoming increasingly poor.
  • a current density above 80 A / dm 2 brings no additional benefit.
  • the duration of the electrochemical treatment is such that the amount of chromium within the chromate layer formed is in the desired range.
  • the amount of chromium is also determined by the concentration of the individual components of the chromating bath, the pH value, the temperature and the current density. If the latter parameters are specified, the electrolysis time required to generate certain chromate layer weights can be determined after a few experiments. Of course, you can also fix the electrolysis time and regulate the layer weight and the chromium content of the layer by changing the current density.
  • the relationship between the amount of electricity per unit area, expressed as Coulomb / dm 2 , and the amount of chromium and silicon deposited in the chromate layer is one in Fig. 1 using the example of the coating reproduced electrolytically galvanized steel sheet.
  • the composition of the chromating bath used was The electrolysis conditions on the basis of which this graph was created are given in Table 7.
  • Table 7 and Fig. 1 demonstrate that the chromate content in the chromate layer produced can easily be controlled by changing the amount of current according to the product of current density and electrolysis time.
  • the content of Si0 2 in the chromate layer is largely independent of the electrochemical conditions and remains practically constant. This makes it clear that the problems of purely chemical chromating processes discussed at the beginning can be eliminated.
  • the layer weight can be increased to improve the corrosion resistance, but at the same time this also increases the silica content, as a result of which the adhesive properties and paintability of the coating formed decrease.
  • chromate layers with excellent corrosion resistance and very good adhesion for a subsequently applied organic coating can be achieved when using the method according to the invention.
  • a preferred embodiment of the invention provides for chromate layers whose chromium content is 10 to 300 mg / m 2 , preferably 20 to 150 mg / m2 (calc. as Cr), and their silica and / or silicate content is 3 to 30 mg / m 2 , preferably 5 to 20 mg / m 2 (calculated as Si).
  • nitrate ions in the chromating bath not only increases the corrosion resistance of the chromate layers formed, but is also responsible for increasing the stability of the chromating bath and thus for the uniformity of the appearance of the chromate layers produced during continuous treatment.
  • the content of nitrate ions largely prevents accumulating zinc and chromium ions from precipitating in the chromating bath.
  • the surfaces of zinc or zinc alloys treated by the process according to the invention are usually rinsed with water and then dried.
  • the chromate layers produced by the process can be post-treated with the usual aqueous chromate solutions and / or with corrosion-protecting solutions based on organic plastics before drying.
  • the chromate layers produced provide excellent corrosion resistance and are an excellent base for subsequent application of organic coatings, such as paints.
  • the method according to the invention intended for the treatment of surfaces made of zinc or zinc alloys is suitable for workpieces made of compact zinc or of compact zinc alloys. It is also suitable for workpieces that have a surface coating of zinc or zinc alloy. This overlay can have been produced, for example, from a melt or electrolysis deposition.
  • the method according to the invention is of particular importance for the treatment of galvanized steel strip.
  • the pH here was 1.2.
  • This chromating bath described in Example 1 was applied to the same cleaned, electrolytically galvanized steel sheet by rolling and dried.
  • the chromium content of the chromate layer was controlled by appropriate metering of the amount of chromate bath applied.
  • the baths were modified with 0.06, 0.12 and 0.24 g / 1 N0 3 ions (introduced via NaN0 3 ) and adjusted to pH 5.0 using sodium hydroxide.
  • Conditions of cathodic electrolysis were modified with 0.06, 0.12 and 0.24 g / 1 N0 3 ions (introduced via NaN0 3 ) and adjusted to pH 5.0 using sodium hydroxide.
  • Example 4 Cleaned sheets of the quality of Example 4 were treated electrolytically with chromating baths, as indicated in Example 4, under the conditions of Example 4. In one case Si0 2 was omitted, in the other the concentration was reduced to 3 g / 1. The results obtained are shown in Table 4.
  • Example 5 Cleaned sheets according to Example 5 were treated with the same chromating baths under the same conditions of cathodic electrolysis as in Example 5, but the additions of Cr 3+ were such that weight ratios of 1: 100 and 1: 2.5 resulted.
  • the samples are shown in Table 5 as Comparative Examples 5.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Coating With Molten Metal (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
EP86115014A 1985-11-01 1986-10-29 Procédé pour obtenir des couches à base de chromate Expired EP0224065B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86115014T ATE40158T1 (de) 1985-11-01 1986-10-29 Verfahren zur erzeugung von chromatschichten.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP244063/85 1985-11-01
JP60244063A JPS62107096A (ja) 1985-11-01 1985-11-01 亜鉛メツキ鋼板の表面処理方法

Publications (2)

Publication Number Publication Date
EP0224065A1 true EP0224065A1 (fr) 1987-06-03
EP0224065B1 EP0224065B1 (fr) 1989-01-18

Family

ID=17113178

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86115014A Expired EP0224065B1 (fr) 1985-11-01 1986-10-29 Procédé pour obtenir des couches à base de chromate

Country Status (9)

Country Link
US (1) US4756805A (fr)
EP (1) EP0224065B1 (fr)
JP (1) JPS62107096A (fr)
AT (1) ATE40158T1 (fr)
AU (1) AU583431B2 (fr)
CA (1) CA1311714C (fr)
DE (2) DE3636797A1 (fr)
NZ (1) NZ217984A (fr)
ZA (1) ZA867143B (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0244022A2 (fr) * 1986-04-26 1987-11-04 Nihon Parkerizing Co., Ltd. Procédé de post-traitement de surfaces métalliques phosphatées

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63143292A (ja) * 1986-12-05 1988-06-15 Nippon Steel Corp 耐食性に優れた電解クロメート処理亜鉛系メッキ鋼板の製造方法
DE3882769T2 (de) * 1987-03-31 1993-11-11 Nippon Steel Corp Korrosionsbeständiges plattiertes Stahlband und Verfahren zu seiner Herstellung.
US4910095A (en) * 1987-12-29 1990-03-20 Nippon Steel Corporation High corrosion resistant plated composite steel strip
US5268112A (en) * 1990-12-21 1993-12-07 Union Oil Company Of California Gel-forming composition
US6592738B2 (en) 1997-01-31 2003-07-15 Elisha Holding Llc Electrolytic process for treating a conductive surface and products formed thereby
US6599643B2 (en) * 1997-01-31 2003-07-29 Elisha Holding Llc Energy enhanced process for treating a conductive surface and products formed thereby
US6322687B1 (en) 1997-01-31 2001-11-27 Elisha Technologies Co Llc Electrolytic process for forming a mineral
WO2003066937A2 (fr) * 2002-02-05 2003-08-14 Elisha Holding Llc Procede pour traiter des surfaces metalliques et produits ainsi realises
US20040188262A1 (en) * 2002-02-05 2004-09-30 Heimann Robert L. Method for treating metallic surfaces and products formed thereby
WO2011102537A1 (fr) * 2010-02-19 2011-08-25 新日本製鐵株式会社 Tôle d'acier galvanisée et son procédé de production

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733199A (en) * 1956-01-31 Electrolytic treatment of metal
US3288691A (en) * 1962-06-13 1966-11-29 Yawata Iron & Steel Co Method of electrolytically chemically treating metals

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU427614A1 (ru) * 1971-10-05 1977-11-05 Ордена Трудового Красного Знамени Институт Химии И Химической Технологии Ан Литовской Сср Состав дл пассисировани цинка
FR2220600B2 (fr) * 1973-03-09 1976-09-10 Mecano Bundy Gmbh
GB1531056A (en) * 1976-06-01 1978-11-01 Bnf Metals Tech Centre Electrolytic production of chromium conversion coatings
US4578122A (en) * 1984-11-14 1986-03-25 Omi International Corporation Non-peroxide trivalent chromium passivate composition and process

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733199A (en) * 1956-01-31 Electrolytic treatment of metal
US3288691A (en) * 1962-06-13 1966-11-29 Yawata Iron & Steel Co Method of electrolytically chemically treating metals

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, Band 83, Nr. 2, 14. Juli 1975, Seite 498, Zusammenfassung Nr. 17702s, Columbus, Ohio, US; & JP-A-74 36 101 (S. SHIMADA et al. ) 27-09-1974 *
CHEMICAL ABSTRACTS, Band 97, Nr. 20, November 1982, Seite 567, Zusammenfassung Nr. 171364d, Columbus, Ohio, US; & SU-A-945 252 (INSTITUTE OF CHEMISTRY AND CHEMICAL TECHNOLOGY, ACADEMY OF SCIENCES, LITHUANIAN S.S.R.) 23-07-1982 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0244022A2 (fr) * 1986-04-26 1987-11-04 Nihon Parkerizing Co., Ltd. Procédé de post-traitement de surfaces métalliques phosphatées
EP0244022A3 (fr) * 1986-04-26 1989-03-15 Nihon Parkerizing Co., Ltd. Procédé de post-traitement de surfaces métalliques phosphatées

Also Published As

Publication number Publication date
ZA867143B (en) 1987-04-29
JPH0124880B2 (fr) 1989-05-15
NZ217984A (en) 1988-11-29
AU583431B2 (en) 1989-04-27
AU6427586A (en) 1987-05-07
DE3661846D1 (en) 1989-02-23
ATE40158T1 (de) 1989-02-15
EP0224065B1 (fr) 1989-01-18
DE3636797A1 (de) 1987-05-07
JPS62107096A (ja) 1987-05-18
CA1311714C (fr) 1992-12-22
US4756805A (en) 1988-07-12

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