EP0224065B1 - Procédé pour obtenir des couches à base de chromate - Google Patents

Procédé pour obtenir des couches à base de chromate Download PDF

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Publication number
EP0224065B1
EP0224065B1 EP86115014A EP86115014A EP0224065B1 EP 0224065 B1 EP0224065 B1 EP 0224065B1 EP 86115014 A EP86115014 A EP 86115014A EP 86115014 A EP86115014 A EP 86115014A EP 0224065 B1 EP0224065 B1 EP 0224065B1
Authority
EP
European Patent Office
Prior art keywords
chromium
chromate
ions
chromating
zinc
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.)
Expired
Application number
EP86115014A
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German (de)
English (en)
Other versions
EP0224065A1 (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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    • 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 of zinc or zinc alloys electrochemically by means of chromium 6+ containing aqueous Chromat michsbäder.
  • a difficulty in setting the desired layer weight is also that either the concentration of the treatment solution varies or z.
  • 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 with 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 produced with the aid of a chromating bath which contains 5 to 70 g / l of chromium 6+ ions, 0.01 to 5.0 g / I chromium 3+ ions, 5 to 100 g / I silicic acid and / or silicate and 0.05 to 10 g / I nitrate ions, the weight ratio of chromium 3+ : chromium 6+ in the range of 1:50 to 1 : 3 lies.
  • the chromium 6+ ions can be introduced into the bath individually or as a mixture via chromic anhydride, ammonium and alkali dichromate.
  • concentration of the chromium 6+ ions is essential in that in the case of a concentration below 5 g / l 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.
  • Chrom3 + - ions by the reduction of chromium + 6 - ion with organic substances, such as alcohol, starch, or tannic acid to introduce. Due to the Chrom3 + content, an increased deposition of the 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 Chrom3 +: Chrom 6+ ratio is below 1:50, the described effect weakens. With a Chrom3 +: Chrom 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 approximately 1 to 100 ⁇ m.
  • concentration below 5 g / l the corrosion resistance and paint adhesion decrease.
  • concentrations above 100 g / 1 no further improvement can be achieved.
  • silicic acid and / or silicates separate out and that too much of the chromating bath is removed 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 / l there is an additional improvement in the characteristics stik 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 chromate layer is produced with the aid of a chromating bath which contains 10 to 50 g / l chromium 6 + ions, 0.05 to 5 g / I chromium 3 + ions, 1 0 to 50 g / 1 silica and / or silicate and 0.1 to 3 g / I nitrate ions.
  • the pH of the chromate bath is not critical. However, it is particularly expedient to generate the chromate layers with the aid of a chromating bath, the pH of which is in the range from 1 to 6. At pH values below 1, the characteristics of the chromate layer do not change, 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 expediently 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 workpiece is switched as a cathode. For this it is necessary that the surface is cleaned beforehand. However, the cleaning is not required to be complete.
  • 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 dimensioned 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 tests. 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.
  • Fig. 1 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 shown in Fig. 1 using the example of the coating of an electrolytically galvanized steel sheet.
  • the composition of the chromating bath used was
  • 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 SiO 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 remedied. In these, 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. Instead, when using the method according to the invention, chromate layers with excellent corrosion resistance and very good adhesion for a subsequently applied organic coating can be achieved.
  • 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 / m 2 (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 the increase in the stability of the chromate bath and thus for the uniformity of the appearance of the chromate layers produced during continuous treatment.
  • the nitrate ion content largely prevents accumulating zinc and chromium ions from precipitating in the chromating bath.
  • the surfaces of zinc or zinc alloys treated by the method according to the invention are usually rinsed with water and then dried.
  • the chromate layers produced by the process can be passivated after drying with the usual aqueous chromate solutions and / or with corrosion-protecting solutions based on organic plastics.
  • the chromate layers produced provide excellent corrosion resistance and are an excellent base for the 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, for example, have been produced from a melt or electrolysis deposition.
  • the method according to the invention is of particular importance for the treatment of galvanized steel strip.
  • Electrolysis time 3 to 12 s. (The electrolysis time was regulated in order to achieve a certain chromium content in the chromate layer.)
  • Electrolysis temperature 50 ° C
  • Electrolysis temperature 30 ° C
  • 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 / l. The results obtained are shown in Table 4.
  • Electrolysis temperature 30 ° C
  • 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.
  • Electrolysis temperature 50 ° C
  • Electrolysis temperature 50 ° C
  • Cellophane adhesive strips with a width of 50 mm were stuck onto the coating, quickly torn off and the amounts of Cr and Si residues in the coating were shown in percent. The cheapest value is 100%.
  • the coating was checked for discoloration with the naked eye and in the 4 stages
  • the rust formation according to JIS-Z-2371 was assessed with the naked eye after a certain period of time specified in the tables and in 4 steps
  • Adhesive properties of the coating layer (coating: commercially available white alkyd melamine lacquer, application 27 to 30 pm)
  • the lacquer coating was scratched with a cutter at a distance of 1 mm to the metallic surface, so that a grid with several scratch marks lying at an angle of 90 ° is created. Then the test sheet was slowly dented by pressing in a ball until a bulge of 7 mm in height was formed. The degree of paint removal was then determined by gluing and tearing off an adhesive tape. The extent of the paint layer removed was examined with the naked eye and in 4 steps

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  • 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)

Claims (6)

1. Procédé de production de couches de chromate sur des surfaces de zinc ou d'alliages de zinc, par voie électrochimique, au moyen de bains de chromatage aqueux contenant du chrome6+, caractérisé en ce qu'on produit les couches de chromate à l'aide d'un bain de chromatage qui contient 5 à 70 g/I d'ions chrome6+, 0,01 à 5,0 g/I d'ions chrome3+, 5 à 100 g/1 d'acide silicique et/ou de silicate ainsi que 0,05 à 10 g/I d'ions nitrate, le rapport pondéral chrome3+:chrome6+ étant dans le domaine de 1:50 à 1:3.
2. Procédé suivant la revendication 1, caractérisé par le fait qu'on produit les couches de chromate à l'aide d'un bain de chromatage qui contient 10 à 50 g/I d'ions chrome6+, 0,05 à 5 g/I d'ions chrome3+, 10 à 50 g/I d'acide silicique et/ou de silicate ainsi que 0,1 à 5 g/I d'ions nitrate.
3. Procédé suivant les revendications 1 ou 2, caractérisé en ce qu'on produit les couches de chromate à l'aide d'un bain de chromatage dont le pH est dans le domaine de 1 à 6 et dont la température est dans le domaine de la température ambiante à 70° C.
4. Procédé suivant les revendications 1, 2 ou 3, caractérisé en ce qu'on ajuste le poids de la couche de chromate par un choix approprié de la densité de courant et de la quantité de courant.
5. Procédé suivant une ou plusieurs des revendications 1 à 4, caractérisé en ce qu'on effectue le traitement électrochimique avec une densité de courant cathodique de 3 à 80 A/dm2.
6. Procédé suivant une ou plusieurs des revendications 1 à 5, caractérisé en ce qu'on produit des couches de chromate dont la teneur en chrome est de 10 à 300 mg/m2, de préférence de 20 à 150 mg/m2 (calc. en Cr) et dont la teneur en acide silicique et/ou en silicate est de 3 à 30 mg/m2, de préférence de 5 à 20 mg/m2 (calc. en Si).
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 EP0224065A1 (fr) 1987-06-03
EP0224065B1 true 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) DE3661846D1 (fr)
NZ (1) NZ217984A (fr)
ZA (1) ZA867143B (fr)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0633465B2 (ja) * 1986-04-26 1994-05-02 日本パ−カライジング株式会社 りん酸塩処理した自動車車体の後処理方法
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
EP0285931B1 (fr) * 1987-03-31 1993-08-04 Nippon Steel Corporation Bande d'acier résistant à la corrosion et procédé de fabrication
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
US20040188262A1 (en) * 2002-02-05 2004-09-30 Heimann Robert L. Method for treating metallic surfaces and products formed thereby
US6866896B2 (en) * 2002-02-05 2005-03-15 Elisha Holding Llc Method for treating metallic surfaces and products formed thereby
JP5130496B2 (ja) * 2010-02-19 2013-01-30 新日鐵住金株式会社 亜鉛系めっき鋼板及びその製造方法

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733199A (en) * 1956-01-31 Electrolytic treatment of metal
GB1044962A (en) * 1962-06-13 1966-10-05 Yawata Iron & Steel Co Producing a protective coating on metal by cathodic coating
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

Also Published As

Publication number Publication date
JPS62107096A (ja) 1987-05-18
DE3661846D1 (en) 1989-02-23
AU6427586A (en) 1987-05-07
ATE40158T1 (de) 1989-02-15
CA1311714C (fr) 1992-12-22
JPH0124880B2 (fr) 1989-05-15
ZA867143B (en) 1987-04-29
EP0224065A1 (fr) 1987-06-03
US4756805A (en) 1988-07-12
AU583431B2 (en) 1989-04-27
NZ217984A (en) 1988-11-29
DE3636797A1 (de) 1987-05-07

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