EP0132722A1 - Method for producing tin-free steel strips having improved lacquer adhesion - Google Patents

Method for producing tin-free steel strips having improved lacquer adhesion Download PDF

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Publication number
EP0132722A1
EP0132722A1 EP84108249A EP84108249A EP0132722A1 EP 0132722 A1 EP0132722 A1 EP 0132722A1 EP 84108249 A EP84108249 A EP 84108249A EP 84108249 A EP84108249 A EP 84108249A EP 0132722 A1 EP0132722 A1 EP 0132722A1
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EP
European Patent Office
Prior art keywords
chromium
electrolytic chromate
cro
chromate treatment
treatment
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.)
Withdrawn
Application number
EP84108249A
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German (de)
English (en)
French (fr)
Inventor
Hajime C/O Research Laboratories Ogata
Kyoko C/O Research Laboratories Yamaji
Shunichi Research Laboratories Tsugawa
Toshio Research Laboratories Ichida
Toshio Research Laboratories Irie
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.)
JFE Steel Corp
Original Assignee
Kawasaki Steel Corp
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 Kawasaki Steel Corp filed Critical Kawasaki Steel Corp
Publication of EP0132722A1 publication Critical patent/EP0132722A1/en
Withdrawn legal-status Critical Current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

  • This invention relates to a method for producing tin-free steel strips or sheets having improved lacquer adhesion.
  • Electrolytic chromate treated steel sheets also known as tin-free steel (TFS) of chromium type have improved properties as can-forming material and are regarded as a substitute for tin plates, and the demand for them is increasing in recent years.
  • TFS tin-free steel
  • TFS has a two-layer coating of metallic chromium and hydrated chromium oxide layers on the surface, it does not possess sufficient weldability.
  • a can is fabricated from a TFS sheet by coating the sheet with an epoxy-phenol resin and cementing the mating edges of the coated sheet with a polyamide adhesive to form a can barrel.
  • TFS cans are not only used for low-temperature packs prepared by packing contents such as carbonated beverage and beer in cans at relatively low temperatures, but also used for the so-called hot packs prepared by packing contents such as fruit juice in cans at relatively high temperatures for sterilization.
  • TFS is also used in those cans requiring a high temperature retorting treatment for sterilization at the end of packing of coffee, for example. In the latter applications, there often occurred accidents of rupture of can barrels.
  • This can barrel rupture occurs in cemented TFS cans during hot packing and retorting treatment because hot water penetrates through the coating at the barrel junction to deteriorate the interfacial adhesion between the lacquer film and the TFS substrate to eventually separate the lacquer film from the TFS.
  • the reverse electrolysis may be carried out in the chromium plating solution or in another aqueous solution containing chromium ion, with similar results with respect to lacquer adhesion.
  • chromium oxide (Cr OX ) layer on reversely electrolyzed steel strips without detracting from subsequent lacquer adhesion.
  • electrolytic chromate treatment may be advantageously carried out in an aqueous chromate solution which contains at least one chromium compound selected from chromic acid anhydride, chromates and dichromates as a main ingredient and at least one selected from sulfuric acid, sulfates, thiocyanates, sulfonic acids, and sulfonates as an assistant ingredient.
  • Tin-free steel strips or sheets are advantageously produced by the steps of chromium plating a thin steel strip through cathodic electrolysis in a chromium ion-containing aqueous solution to form a layer consisting essentially of metallic chromium, reversely electrolyzing the chromium plated steel strip by a successive anodizing treatment in said aqueous solution or in another chromium ion-containing aqueous solution, and subjecting the reversely electrolyzed steel strip to an electrolytic chromate treatment in an aqueous solution containing as a main ingredient at least one selected from the group consisting of chromic acid, chromates, and dichromates.
  • the electrolytic chromate treatment should be carried out in the solution which contains as a main ingredient at least one selected from the group consisting of chromic acid, chromates, and dichromates, and as an assistant ingredient at least one selected from the group consisting of sulfuric acid, sulfates, thiocyanates, sulfonic acids and sulfonates, and has a molar ratio of H 2 SO 4 /CrO 3 in the range between 1/1000 and 1/100 provided that the main and assistant ingredients are converted into CrO 3 and H 2 SO 4 , respectively.
  • the present invention is directed to TFS strips or sheets having a layer of metallic chromium (Cr M ) ranging from 50 to 200 mg per square meter on each sheet surface and a layer of hydrated chromium oxides (Cr OX ) ranging from 8 to 30 mg of Cr per square meter on the metallic chromium layer.
  • TFS sheets generally have a metallic chromium layer of 50 to 200 mg/m 2 because thinner layers of less than 50 mg/m 2 have poor corrosion resistance. Thicker layers exceeding 200 mg/m 2 do not provide an additional improvement in corrosion resistance.
  • TFS sheets have a layer of hydrated chromium oxides of 8 to 30 mg/m 2 (calculated as metallic chromium) because thinner layers of less than 8 mg/m 2 do not provide the necessary lacquer adhesion. Thicker layers exceeding 30 mg/m 2 have a poor appearance and are prone to cracking during subsequent processing and thus impractical.
  • the chromate solution in which the electrolytic chromate treatment was carried out contains as a main ingredient at least one chromium compound selected from chromic anhydride, chromates and dichromates.
  • chromium compound selected from chromic anhydride, chromates and dichromates.
  • examples of the chromates and dichromates used herein include potassium chromate K 2 CrO 4 , sodium chromate Na 2 Cr0 4 , ammonium chromate (NH 4 ) 2 CrO 4 , potassium dichromate K 2 Cr 2 O 7 , sodium dichromate Na 2 Cr 2 O 7 , and ammonium dichromate (NH 4 ) 2 Cr 2 O 7 .
  • concentration of the chromium compound should be limited to the range of 20 to 200 g of CrO 3 per liter of the solution.
  • the assistant ingredient which is intentionally added to the chromate solution is at least one compound which is selected from the group consisting of sulfuric acid, sulfates, thiocyanates, sulfonic acids, and sulfonates.
  • the sulfates, thiocyanates, and sulfonic acids and sulfonates used herein include potassium sulfate K 2 SO 4 , sodium sulfate Na 2 S0 4 , and ammonium sulfate (NH4) 2 SO 4 ; potassium thiocyanate KSCN, sodium thiocyanate NaSCN, and ammonium thiocyanate NH 4 SCN; and phenoldisulfonic acid and catecholdisulfonic acid and the potassium, sodium, and ammonium salts thereof.
  • the following experiment was carried out to determine the optimum range of the assistant ingredient concentration in the chromate solution.
  • the assistant ingredient is converted into H 2 S0 4 for calculation purpose.
  • the molar ratio of H 2 SO 4 /CrO 3 was varied over the range between 1/2000 and 3/100.
  • a number of reversely electrolyzed steel pieces were electrolytically chromated.
  • the amount of hydrated chromium oxides (Cr OX ) formed thereon was determined and lacquer adhesion was tested.
  • Fig. 2 shows that the assistant ingredient should be present in such concentrations that the molar ratio of H 2 SO 4 to Cr03 is in the range between 1/1000 and 1/100.
  • region I where the assistant ingredient is present in concentrations to give a molar ratio of H 2 SO 4 /CrO 3 of lower than 1/1000, the assistant ingredient is not effective to assist a chromium oxide layer in growing, failing to achieve the objects of the invention.
  • region III where the assistant ingredient is present in concentrations to give a molar ratio of H 2 S0 4/ Cr0 3 of higher than 1/100, the ' chromate film is stained so that the resulting products become commercially unacceptable.
  • the assistant ingredient should be added to the chromate solution in an amount (calculated as H 2 SO 4 ) such as to give a molar ratio of H 2 SO 4 /CrO 3 between 1/1000 and 1/100 as shown by hatched region II in Fig. 2.
  • the present invention is directed to a method for producing a tin-free steel strip comprising chromium plating, reverse electrolysis, and electrolytic chromate treatment. Unless the reverse electrolysis is interposed between the chromium plating and electrolytic chromate treatment, tin-free steel strips having improved lacquer adhesion cannot be obtained even if the electrolytic chromate bath contains the assistant ingredient in a concentration to give a molar ratio of H 2 SO 4 /CrO 3 in the range between 1/1000 and 1/100.
  • a phenol-epoxy lacquer was applied to one surface of a treated steel sheet 1 to a build-up of 60 mg/m 2 and baked for 12 minutes at 210°C to form a lacquer film lA.
  • the same lacquer was applied to one surface of another treated steel sheet 2 to a build-up of 25 mg/m 2 and baked under the same conditions to form another lacquer film 2A.
  • the sheets were cut into pieces of 70 mm wide by 60 mm long. The longitudinal ends of two different pieces were overlapped each other over a distance of 8 mm with a nylon film 3 of 100 1 m thick interposed therebetween as shown in Fig. 3a.
  • a phenol-epoxy lacquer was applied to a treated steel sheet to a build up of 50 mg/m 2 and baked for 12 minutes at 210°C. The baked sheet was cut into pieces of 5 mm wide. A sandwich of two pieces with a nylon adhesive interposed between the lacquer films was cemented under a hot press at 200°C for 30 seconds. The cemented samples were immersed for 7 days in a 0.4% citric acid aqueous solution at 90°C. Thereafter, T-peel tensile strength was measured to evaluate secondary or wet adhesion of lacquer. In this T-peel test, samples whose T-peel tensile strength was 2.5 kg/5 mm or more after 7-day immersion in 0.4% citric acid solution at 90°C were evaluated good.
  • T4CA Cold rolled steel sheets having a thickness of 0.22 mm were electrolytically degreased in a 5% homezarine solution at 80°C, rinsed with water, immersed in a 10% H 2 S0 4 for 5 seconds for pickling, rinsed again with water, and then subjected to the following treatments in sequence:
  • Steps (1) and (2) were successively carried out in the same electrolytic bath. These steps were carried out in the following conditions.
  • the steel sheets were subjected to reverse electrolysis at a current density of 5 A/dm 2 for 0.2 seconds or at a current density of 15 A/dm 2 for 0.1 seconds while the sheet was made the anode in the same bath as used for chromium plating. For comparison sake, some steel sheets were not subjected to reverse electrolysis.
  • Cathodic treatment was carried out with an electricity quantity of 10 to 20 coulomb/dm 2 using various chromate baths based on CrO 3 and Na 2 Cr 2 O 7 and containing varying concentrations of the assistant (H 2 SO 4 ) at a temperature of 40°C.
  • one chromate bath was free of H 2 SO 4 .
  • TFS sheets By carrying out (1) chromium plating, (2) reverse electrolysis, and (3) electrolytic chromate treatment in succession, there were prepared TFS sheets.
  • the amount of chromium oxides (Cr OX ) formed on the TFS sheets was determined by X-ray fluorometry and the amount of metallic chromium (Cr M ) was determined by electrolytic analysis.
  • the U- and T-peel tests were carried out to evaluate lacquer adhesion after retorting. The results are shown in Table 1.'
  • Example 1 chromium plating (1) is followed by reverse electrolysis (2) and then by electrolytic chromate treatment in a bath containing H 2 S0 4 in such a lower concentration as to give a molar ratio of H 2 SO 4 /CrO 3 of 1/2000.
  • Example 2 used an electrolytic chromate bath having a proper H 2 S0 4 concentration to give a molar ratio of H 2 SO 4 /CrO 3 of 1/200, yielding a sufficient quantity of chromium oxide (Cr OX ) which ensures the improved wet lacquer adhesion.
  • Example 3 (comparison) used an electrolytic chromate bath having the same H 2 SO 4/ CrO 3 ratio as in Example 2, but omitted reverse electrolysis (2).
  • the elimination of reverse electrolysis (2) resulted in inferior wet lacquer adhesion irrespective of an increased quantity of chromium oxide.
  • Example 4 (comparison) carried out chromium plating (1) and reverse electrolysis (2) followed by electrolytic chromate treatment in a bath containing H 2 S0 4 in such a higher concentration as to give a molar ratio of H 2 SO 4 /CrO 3 of 2/100. Although wet lacquer adhesion was satisfactory, products were stained to a commercially unacceptable level.
  • chromium plating (1) and reverse electrolysis (2) were followed by electrolytic chromate treatment in a bath having a molar ratio of H 2 SO 4 /CrO 3 in the range of 1/1000 to 1/100, that is, the specific range according to the present invention. Sufficient quantities of chromium oxide were present and the wet lacquer adhesion was superior.
  • Examples 8 and 9 (comparison) carried out reverse electrolysis (anodic treatment) (2) and electrolytic chromate treatment (cathodic treatment) (3) without chromium plating (cathodic treatment) (1), failing to provide improved lacquer adhesion.

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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)
  • Electroplating Methods And Accessories (AREA)
  • Electrochemical Coating By Surface Reaction (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
EP84108249A 1983-07-20 1984-07-13 Method for producing tin-free steel strips having improved lacquer adhesion Withdrawn EP0132722A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP13207183A JPS6024399A (ja) 1983-07-20 1983-07-20 塗料密着性にすぐれたテインフリ−鋼板の製造方法
JP132071/83 1983-07-20

Publications (1)

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EP0132722A1 true EP0132722A1 (en) 1985-02-13

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EP84108249A Withdrawn EP0132722A1 (en) 1983-07-20 1984-07-13 Method for producing tin-free steel strips having improved lacquer adhesion

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EP (1) EP0132722A1 (ja)
JP (1) JPS6024399A (ja)
CA (1) CA1238293A (ja)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0194654A1 (en) * 1985-03-15 1986-09-17 Kawasaki Steel Corporation Tin-free steel strips useful in the manufacture of welded cans and process for making
EP0250792A1 (en) * 1986-05-12 1988-01-07 Nippon Steel Corporation A chromate treatment of a metal coated steel sheet

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3679554A (en) * 1969-01-13 1972-07-25 Nippon Kokan Kk Method for electrolytic treatment of steel surface in a chromate solution
US3986940A (en) * 1975-02-04 1976-10-19 Nippon Kokan Kabushiki Kaisha Process for manufacturing electrolytically chromated steel sheet

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3679554A (en) * 1969-01-13 1972-07-25 Nippon Kokan Kk Method for electrolytic treatment of steel surface in a chromate solution
US3986940A (en) * 1975-02-04 1976-10-19 Nippon Kokan Kabushiki Kaisha Process for manufacturing electrolytically chromated steel sheet

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, unexamined applications, C field, vol. 4, no. 61, May 8, 1980 THE PATENT OFFICE JAPANESE GOVERNMENT page 50 c 9 & JP-A-55-28 309 (shin nippon seitetsu k.k.) *
PATENT ABSTRACTS OF JAPAN, unexamined applications, C field, vol. 7, no. 22, January 28, 1983 THE PATENT OFFICE JAPANESE GOVERNMENT page 55 C 148 & JP-A-57-177 998 (kawasaki seitetsu k.k.) *
PATENT ABSTRACTS OF JAPAN, unxamined applications, C field, vol. 4, no. 98, July 15, 1980 THE PATENT OFFICE JAPANESE GOVERNMENT page 13 C 18 & JP-A-55-58 395 (kawasaki seitetsu k.k.) *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0194654A1 (en) * 1985-03-15 1986-09-17 Kawasaki Steel Corporation Tin-free steel strips useful in the manufacture of welded cans and process for making
US4687713A (en) * 1985-03-15 1987-08-18 Kawasaki Steel Corporation Tin-free steel strips useful in the manufacture of welded cans and process for making
EP0250792A1 (en) * 1986-05-12 1988-01-07 Nippon Steel Corporation A chromate treatment of a metal coated steel sheet

Also Published As

Publication number Publication date
JPS6024399A (ja) 1985-02-07
CA1238293A (en) 1988-06-21

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Inventor name: TSUGAWA, SHUNICHIRESEARCH LABORATORIES

Inventor name: OGATA, HAJIMEC/O RESEARCH LABORATORIES

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Inventor name: YAMAJI, KYOKOC/O RESEARCH LABORATORIES