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
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
• • 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
• • 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
  • C23C22/361—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 titanium, zirconium or hafnium 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
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
• • 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
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/562—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of iron or nickel or cobalt
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
  • C25D5/50—After-treatment of electroplated surfaces by heat-treatment
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated
  • C25D7/06—Wires; Strips; Foils
  • C25D7/0614—Strips or foils
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D9/00—Electrolytic coating other than with metals
  • C25D9/04—Electrolytic coating other than with metals with inorganic materials
  • C25D9/08—Electrolytic coating other than with metals with inorganic materials by cathodic processes

Definitions

• the present disclosure relates to surface-treated steel sheets, and in particular to surface-treated steel sheets with excellent adhesion to BPA (bisphenol A)-free paint.
• the surface-treated steel sheet of the present disclosure can be suitably used in containers such as cans.
• the present disclosure also relates to a method of producing the surface-treated steel sheet.
• a Sn plating steel sheet (tinplate), one type of surface-treated steel sheet, is widely used as material for various metal cans such as beverage cans, food cans, pails, and 18-liter cans because of its excellent corrosion resistance, weldability, workability, and ease of production.
• BPA-free paint using polyester-based resins that do not contain BPA are being developed (PTL 6, 7), and demand exists for replacing epoxy-based paint.
• tinplate which has been used as steel sheets for cans, has poor adhesion to BPA-free paint compared to adhesion to epoxy-based paint. Therefore, the application of BPA-free paint to various metal cans has not progressed due to insufficient corrosion resistance to various contents.
• a surface treatment layer can be formed without using hexavalent chromium. Also according to PTL 8, the above method can obtain a surface-treated steel sheet with excellent adhesion to epoxy-based paint.
• the surface-treated steel sheet obtained by the conventional method as proposed in PTL 8 has poor adhesion to BPA-free paint, resulting in insufficient BPA-free paint corrosion resistance. Replacement with BPA-free paint while ensuring corrosion resistance to various contents has therefore not been possible.
• a surface-treated steel sheet that uses no hexavalent chromium and that has excellent adhesion to BPA-free paint can be provided.
• the surface-treated steel sheet of the present disclosure can be suitably used as a material for containers and the like.
• a surface-treated steel sheet in an embodiment of the present disclosure includes, on at least one side of the steel sheet, a Ni-containing layer and a coating layer disposed on the Ni-containing layer, the coating layer containing at least one of Zr oxide and Ti oxide.
• any steel sheet can be used as the above steel sheet without any particular limitation, but a steel sheet for cans is preferred.
• a steel sheet for cans is preferred.
• an ultra low carbon steel sheet or low carbon steel sheet can be used as the steel sheet.
• the method of producing the steel sheet is not limited, and a steel sheet produced by any method may be used, but it typically suffices to use a cold-rolled steel sheet.
• the cold-rolled steel sheet can be produced by general production processes, for example, hot rolling, pickling, cold rolling, annealing, and temper rolling.
• the chemical composition of the steel sheet is not limited, but the steel sheet may contain C, Mn, Cr, P, S, Si, Cu, Ni, Mo, Al, and unavoidable impurities to the extent that the effects of the scope of the present disclosure are not impaired.
• a steel sheet with the chemical composition specified in ASTM A623M-09, for example, can be suitably used as the steel sheet.
• the Ni-containing layer need only be provided on at least one side of the steel sheet but may be provided on both sides.
• the Ni-containing layer need only cover at least a portion of the steel sheet but may cover the entire side on which the Ni-containing layer is provided.
• the Ni-containing layer may be a continuous layer or a discontinuous layer.
• the discontinuous layer is, for example, a layer with an island-like structure.
• any layer that contains nickel can be used.
• a Ni layer and a Ni alloy layer can be used.
• the case of a Ni alloy layer resulting from diffusion annealing treatment after Ni plating is also considered a Ni alloy layer.
• the Ni alloy layer is, for example, a Ni-Fe alloy layer.
• the Ni-containing layer is preferably a Ni-based plating layer.
• the "Ni-based plating layer” is defined as a plating layer with a Ni content of 50 mass% or more.
• the Ni-based plating layer is a Ni plating layer or a plating layer consisting of Ni-based alloy.
• the Ni-based plating layer may be a dispersion plating layer (composite plating layer) in which solid fine particles are dispersed in Ni or a Ni-based alloy as a matrix.
• the fine particles may be either inorganic fine particles or organic fine particles.
• the organic fine particles include, for example, fine particles made of resin. Any resin can be used as the resin, but fluororesin is preferably used, and polytetrafluoroethylene (PTFE) is more preferably used.
• PTFE polytetrafluoroethylene
• the inorganic fine particles fine particles made of any inorganic material can be used without any limitation.
• the inorganic material may, for example, be a metal (including alloys), a compound, or other single substance.
• fine particles including at least one selected from the group consisting of oxides, nitrides, and carbides are preferably used, and fine particles of metal oxides are preferably used.
• the metal oxides include aluminum oxide, chromium oxide, titanium oxide, and zinc oxide.
• the Ni coating weight in the Ni-containing layer is not limited and can be any amount. However, from the perspective of further improving the appearance and corrosion resistance of the surface-treated steel sheet, the Ni coating weight is preferably set to 20.0 g/m 2 or less per side of the steel sheet. From the same perspective, the Ni coating weight is preferably set to 0.1 g/m 2 or more and more preferably to 0.2 g/m 2 or more. From the perspective of further improving workability, the Ni coating weight is even more preferably set to 1.0 g/m 2 or more.
• the Ni coating weight of the Ni-containing layer is measured by a calibration curve method using X-ray fluorescence.
• a plurality of steel sheets with known Ni coating weight are prepared, the X-ray fluorescence intensity derived from Ni is measured for the plates in advance, and the relationship between the measured X-ray fluorescence intensity and the Ni coating weight is linearly approximated to yield a calibration curve.
• the X-ray fluorescence intensity derived from Ni in the surface-treated steel sheet can then be measured, and the above-described calibration curve can be used to determine the Ni coating weight of the Ni-containing layer.
• the method of forming the Ni-containing layer is not limited, and any method, such as electroplating, can be used.
• the Ni-Fe alloy layer can be formed by forming a Ni layer on the steel sheet surface, by electroplating or another such method, and then annealing.
• the surface side of the Ni-containing layer may contain Ni oxide or may contain no Ni oxide at all.
• the surface side of the Ni-containing layer preferably does not contain Ni oxide.
• Ni oxide can be formed by dissolved oxygen contained in water used in water washing after Ni plating, the Ni oxide contained in the Ni-containing layer is preferably removed by the below-described pretreatment or the like.
• a coating layer containing at least one of Zr oxide and Ti oxide exists on the Ni-containing layer.
• the inclusion of at least one of Zr oxide and Ti oxide in the coating layer is necessary to obtain excellent adhesion to BPA-free paint.
• the total coating weight of the Zr oxide and Ti oxide is preferably 0.3 mg/m 2 or more, more preferably 0.4 mg/m 2 or more, and even more preferably 0.5 mg/m 2 or more, per side of the steel sheet in terms of the amount of metal Zr and amount of metal Ti.
• No upper limit is placed on the total coating weight of Zr oxide and Ti oxide in the coating layer either. However, if the total coating weight of Zr oxide and Ti oxide is excessively high, the adhesion to the BPA-free paint may be compromised due to cohesion failure of the coating layer.
• the total coating weight of the Zr oxide and Ti oxide is preferably 50.0 mg/m 2 or less, more preferably 45.0 mg/m 2 or less, and even more preferably 40.0 mg/m 2 or less, per side of the steel sheet in terms of the amount of metal Zr and amount of metal Ti.
• the value yielded by conversion to the amount of metal Zr is used as the coating weight of Zr oxide
• the value yielded by conversion to the amount of metal Ti is used as the coating weight of Ti oxide.
• the coating weight of Ti oxide in the coating layer is also measured by a calibration curve method using X-ray fluorescence.
• a calibration curve method using X-ray fluorescence First, a plurality of steel sheets with known Ti coating weight are prepared, the X-ray fluorescence intensity derived from Ti is measured for the plates in advance, and the relationship between the measured X-ray fluorescence intensity and the coating weight as metal Ti is linearly approximated to yield a calibration curve.
• the X-ray fluorescence intensity derived from Ti in the surface-treated steel sheet can then be measured, and the above-described calibration curve can be used to determine the coating weight of Ti oxide in the coating layer in terms of metal Ti.
• the coating layer may contain P from the perspective of further improving adhesion to BPA-free paint.
• the coating weight of P is preferably 50.0 mg/m 2 or less per side of the steel sheet, since adhesion to BPA-free paint may be impaired due to cohesion failure of the coating layer.
• No lower limit is placed on the coating weight of P in the coating layer, and the coating weight of P may, for example, be 0.0 mg/m 2 , i.e., no P whatsoever may be contained.
• the coating weight of P in the coating layer is measured by a calibration curve method using X-ray fluorescence.
• a plurality of steel sheets with known P coating weight are prepared, the X-ray fluorescence intensity derived from P is measured for the plates in advance, and the relationship between the measured X-ray fluorescence intensity and the P coating weight is linearly approximated to yield a calibration curve.
• the X-ray fluorescence intensity derived from P in the surface-treated steel sheet can then be measured, and the above-described calibration curve can be used to determine the coating weight of P in the coating layer.
• the coating weight of Mn in the coating layer is measured by a calibration curve method using X-ray fluorescence.
• a plurality of steel sheets with known Mn coating weight are prepared, the X-ray fluorescence intensity derived from Mn is measured for the plates in advance, and the relationship between the measured X-ray fluorescence intensity and the Mn coating weight is linearly approximated to yield a calibration curve.
• the X-ray fluorescence intensity derived from Mn in the surface-treated steel sheet can then be measured, and the above-described calibration curve can be used to determine the coating weight of Mn in the coating layer.
• the aforementioned coating layer may contain C. No upper limit is placed on the C content in the coating layer.
• the coating layer need not contain C, i.e., the content may be 0.0 mg/m 2 .
• the aforementioned coating layer may contain elements other than Zr, Ti, O, Ni, Mn, P and C, along with the below-described K, Na, Mg, and Ca.
• Elements other than those described above include metallic impurities such as Cu, Zn, and Fe, and elements such as S, N, F, Cl, Br, and Si, contained in the aqueous solution used in the coating formation process described below.
• an excessive presence of elements other than Zr, Ti, O, Ni, Mn, P, C, K, Na, Mg, and Ca may reduce adhesion to BPA-free paint.
• the total content of elements other than Zr, Ti, O, Ni, Mn, P, C, K, Na, Mg, and Ca in the coating layer is preferably 30 % or less, and more preferably 20 % or less, in atomic ratio.
• the coating layer need not contain elements other than Zr, Ti, O, Ni, Mn, P, C, K, Na, Mg, and Ca, i.e., the content may be 0 % in atomic ratio.
• the content of the above elements can be measured by XPS (X-ray photoelectron spectroscopy).
• the contact angle of ethylene glycol on the surface-treated steel sheet be 50° or less.
• the contact angle of ethylene glycol is preferably set to 48° or less, and even more preferably to 45° or less. No lower limit is placed on the contact angle of ethylene glycol, and the contact angle may be 0°, because a lower contact angle is preferable from the perspective of improving adhesion to BPA-free paint.
• the contact angle may be 5° or more, or 8° or more.
• the surface of the surface-treated steel sheet in the present disclosure i.e., the surface of the coating layer containing at least one of Zr oxide and Ti oxide
• the contact angle of ethylene glycol does not change significantly after heat treatment equivalent to paint baking. It is assumed that such thermal stability of the surface state also contributes to improved adhesion to BPA-free paint. Therefore, the contact angle of ethylene glycol on the surface-treated steel sheet after heat treatment equivalent to painting is also preferably 50° or less, more preferably 48° or less, and even more preferably 45° or less.
• No lower limit is placed on the contact angle of the surface-treated steel sheet after heat treatment equivalent to painting, and the contact angle may be 0°, but the contact angle may be 5° or more, or 8° or more.
• the conditions of the heat treatment equivalent to painting are set to a maximum temperature of 200 °C and a holding time at the maximum temperature of 10 minutes.
• the mechanism by which the contact angle of ethylene glycol on the surface-treated steel sheets becomes 50° or less is not clear, it is believed that the surface is modified to have a high affinity for ethylene glycol by adjustment of the surface micro-roughness in the surface conditioning process described below.
• the surface conditioning process described below is not performed, the aforementioned coating layer cannot be fixed in a state with the aforementioned high affinity, and the contact angle of ethylene glycol exceeds 50°, even if the surface of the surface-treated steel sheet has high affinity for ethylene glycol immediately after production.
• the contact angle of ethylene glycol can be measured by the ⁇ /2 method.
• the temperature of the surface-treated steel sheet to be measured is set to 20 °C, and ethylene glycol at a temperature of 20 °C is dropped onto the surface of the surface-treated steel sheet.
• the contact angle after 1 second from dropping is calculated by the 0/2 method. More specifically, measurement can be made by the method described in the Examples.
• the surface of the surface-treated steel sheet may be coated with an anti-rust oil such as CSO (Cottonseed Oil), DOS (Dioctyl Sebacate), and ATBC (Acetyl Tributyl Citrate).
• additives such as rust inhibitors contained in the painted oil may remain on the surface of the surface-treated steel sheet after heat treatment equivalent to painting, the amount thereof is so small that it does not affect the above-described contact angle of ethylene glycol and atomic ratio of adsorbed elements.
• the contact angle of ethylene glycol on the surface-treated steel sheet of the present disclosure is 50° or less, and the surface is chemically active. Therefore, cations of elements such as K, Na, Mg, and Ca are easily adsorbed on the surface of the surface-treated steel sheet.
• simply setting the contact angle of ethylene glycol to 50° or less does not achieve the intended adhesion, due to the effect of the adsorbed cations.
• the adhesion to BPA-free paint can be improved in the present disclosure by reducing the amount of the cations adsorbed on the surface of the surface-treated steel sheet.
• the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet to all elements is 5.0 % or less, preferably 3.0 % or less, and more preferably 1.0 % or less.
• the total atomic ratio can be measured by XPS. In the measurement, it suffices to determine the atomic ratios of K, Na, Mg, and Ca to all elements from the integrated intensity of the narrow spectra of K2p, Nals, Ca2p, and Mgls at the top surface of the surface-treated steel sheet, using the relative sensitivity factor method.
• a surface-treated steel sheet with the aforementioned characteristics can be produced by the method described below.
• a method of producing a surface-treated steel sheet in an embodiment of the present disclosure is a method of producing a surface-treated steel sheet that includes, on at least one side of the steel sheet, a Ni-containing layer and a coating layer disposed on the Ni-containing layer, and the method includes the following processes (1) to (3). Each process is described below.
• the surface of a steel sheet having a Ni-containing layer on at least one side is treated with an aqueous solution containing at least one of Zr ions and Ti ions to form a coating layer on the Ni-containing layer.
• the formed coating layer is a coating layer containing at least one of Zr oxide and Ti oxide.
• the treatment with an aqueous solution is not limited and may be performed by any method.
• the treatment can, for example, be performed by electrolysis.
• the steel sheet with the Ni-containing layer is preferably subjected to cathodic electrolysis in the aqueous solution.
• Conventional equipment used for chromating treatment or the like can be used as is for the cathodic electrolysis. Therefore, from the perspective of equipment cost reduction, the coating layer is preferably formed by cathodic electrolysis.
• the method of preparing the aqueous solution is not limited.
• the aqueous solution can be prepared by dissolving one or both of a Zr-containing compound as a Zr ion source and a Ti-containing compound as a Ti ion source in water. Distilled water or deionized water can be used as the water, but these examples are not limiting, and any water can be used.
• Zr salts such as ZrF 4 or Zr complexes such as H 2 ZrF 6 and K 2 ZrF 6 are preferably used as the Zr-containing compound.
• Zr ions become Zr oxide and form a coating.
• Ti salts such as TiF 4 or Ti complexes such as H 2 TiF 6 and K 2 TiF 6 are preferably used as the Ti-containing compound.
• Ti ions become Ti oxide and form a coating.
• the aqueous solution contains Zr ions
• the concentration is preferably set to 100 ppm or more.
• the concentration is preferably set to 4000 ppm or less.
• the aqueous solution contains Ti ions
• no lower limit is placed on the concentration of the Ti ions, but the concentration is preferably set to 100 ppm or more.
• the concentration is preferably set to 4000 ppm or less.
• the aqueous solution contains fluorine ions
• the concentration is preferably set to 120 ppm or more.
• No upper limit is placed on the concentration of the fluorine ions either, but the concentration is preferably set to 4000 ppm or less.
• the aqueous solution contains phosphate ions
• no lower limit is placed on the concentration of the phosphate ions, but the concentration is preferably set to 50 ppm or more.
• No upper limit is placed on the concentration of the phosphate ions either, but the concentration is preferably set to 5000 ppm or less.
• the aqueous solution contains Mn ions
• the concentration is preferably set to 50 ppm or more.
• No upper limit is placed on the concentration of the Mn ions either, but the concentration is preferably set to 5000 ppm or less.
• the aqueous solution contains ammonium ions
• no lower limit is placed on the concentration of the ammonium ions, and the concentration may be 0 ppm.
• No upper limit is placed on the concentration of the ammonium ions either, but the concentration is preferably set to 20000 ppm or less.
• the aqueous solution contains nitrate ions
• no lower limit is placed on the concentration of the nitrate ions, and the concentration may be 0 ppm.
• No upper limit is placed on the concentration of the nitrate ions either, but the concentration is preferably set to 20000 ppm or less.
• the aqueous solution contains sulfate ions
• no lower limit is placed on the concentration of the sulfate ions
• the concentration may be 0 ppm.
• No upper limit is placed on the concentration of the sulfate ions either, but the concentration is preferably set to 20000 ppm or less.
• No upper limit is placed on the temperature of the aqueous solution during cathodic electrolysis, but the temperature is preferably set to 50 °C or lower, for example.
• Cathodic electrolysis at temperatures of 50 °C or lower enables the formation of a dense, uniform coating microstructure constituted by very fine particles.
• the temperature of the aqueous solution is preferably set to 10 °C or higher, for example.
• the efficiency of coating formation can be increased.
• the temperature of the aqueous solution is 10 °C or higher, cooling of the solution is not necessary even when the outside temperature is high, such as during the summer, which is economical.
• No lower limit is placed on the pH of the aqueous solution, but the pH is preferably set to 3 or higher. If the pH is 3 or higher, the formation efficiency of Zr oxide or Ti oxide can be further improved.
• No upper limit is placed on the pH of the aqueous solution either, but the pH is preferably set to 5 or less. A pH of 5 or less prevents the formation of large amounts of precipitation in the aqueous solution and can achieve good continuous productivity.
• the current density for cathodic electrolysis is, for example, preferably set to 0.05 A/dm 2 or higher, more preferably 1 A/dm 2 or higher. If the current density is 0.05 A/dm 2 or higher, the formation efficiency of Zr oxide or Ti oxide is improved. As a result, a more stable coating layer containing Zr oxide or Ti oxide can be generated, further improving adhesion to BPA-free paint.
• No upper limit is placed on the current density during cathodic electrolysis, but the current density is, for example, preferably set to 50 A/dm 2 or less, more preferably 10 A/dm 2 or less. If the current density is 50 A/dm 2 or less, the efficiency of generating Zr oxides or Ti oxides can be made appropriate, and the generation of coarse Zr oxide or Ti oxide with poor adhesion can be suppressed.
• the current pattern in the aforementioned cathodic electrolysis may be continuous current passage or intermittent current passage.
• the relationship between the aqueous solution and the steel sheet during the aforementioned cathodic electrolysis is not limited, and the solution may be relatively stationary or moving.
• cathodic electrolysis is preferably conducted while the steel sheet and the aqueous solution are moved relative to each other.
• cathodic electrolysis can be performed continuously while passing a steel sheet through a treatment tank housing an aqueous solution containing at least one of Zr ions and Ti ions, so that the steel sheet and the aqueous solution are moved relative to each other.
• the relative flow speed between the aqueous solution and the steel sheet is preferably 50 m/min or more. If the relative flow speed is 50 m/min or more, the pH of the steel sheet surface where hydrogen is generated together with current passage can be made more uniform, effectively suppressing the formation of coarse Zr oxide or Ti oxide. No upper limit is placed on the relative flow speed.
• the coating layer obtained in the coating formation process is surface conditioning. Specifically, the aqueous solution is held at 1.0 g/m 2 to 30.0 g/m 2 on a surface of the coating layer for 0.1 seconds to 20.0 seconds.
• the coating layer can be fixed in a state with a high affinity for ethylene glycol.
• the aqueous solution is preferably in the form of a liquid film from the perspective of ensuring uniform progress of etching.
• the amount of the aforementioned aqueous solution can be measured by a moisture meter using a filter-type infrared absorption method. Specifically, the absorbance at the surface is measured by a moisture meter using a filter-type infrared absorption method, and the amount of aqueous solution is determined from the absorbance using a previously determined calibration curve.
• the calibration curve can be prepared by the following procedures. First, a steel sheet with the above coating layer is placed on an electronic balance. The aqueous solution is dropped by pipette onto the steel sheet having the coating layer to form a liquid film over the entire surface of the steel sheet having the coating layer.
• the weight of the aqueous solution present on the steel sheet having the coating layer is determined from the weight of the steel sheet having the coating layer before the aqueous solution is dropped and the weight of the steel sheet having the coating layer after the aqueous solution is dropped.
• the resulting weight of the aqueous solution is divided by the area of the steel sheet having the coating layer to obtain the amount of aqueous solution per unit area.
• the absorbance on the surface of the steel sheet having the coating layer is measured by a moisture meter using a filter-type infrared absorption method.
• the above measurements are performed multiple times while varying the amount of aqueous solution, and a calibration curve representing the correlation between the amount of aqueous solution and absorbance is created. A linear approximation of the correlation between the amount of aqueous solution and absorbance can be used as the calibration curve.
• the method of adjusting the amount of aqueous solution present on the surface of the coating layer is not limited, and any method can be used.
• the amount of the aqueous solution on the surface of the steel sheet can be adjusted by wringing out the solution with a wringer roll or by wiping.
• No upper limit is placed on the concentration of sulfate ions contained in the aqueous sulfuric acid solution, but the concentration is preferably 200 g/L or lower, more preferably 150 g/L or lower.
• concentration is preferably 200 g/L or lower, more preferably 150 g/L or lower.
• concentration is preferably 200 g/L or lower, more preferably 150 g/L or lower.
• temperature is preferably 10 °C or higher, more preferably 15 °C or higher.
• No upper limit is placed on the temperature of the aqueous sulfuric acid solution, but the temperature is preferably 70 °C or lower, more preferably 60 °C or lower.
• water washing is preferably performed from the perspective of removing any pretreatment solution adhering to the surface.
• pretreatment is preferably performed on the base steel sheet.
• any of the above pretreatments can be performed, at least one of degreasing, pickling, and water washing is preferably performed.
• Pickling removes the natural oxide film present on the surface of the steel sheet and activates the surface.
• the pickling is not limited and can be performed by any method. After pickling, water washing is preferably performed to remove any pickling treatment solution adhering to the steel sheet surface.
• the steel sheet after the surface conditioning process is subjected to water washing at least once.
• Water washing removes any residual aqueous solution from the surface of the steel sheet.
• the water washing is not limited and may be performed by any method.
• a water washing tank can be installed downstream from the tank for coating formation, and the steel sheet after the coating formation process can be continuously immersed in water. Water washing may also be performed by spraying water on the steel sheet after the coating formation process.
• water with an electrical conductivity of 100 ⁇ S/m or less at least in the last water washing of the water washing process. This reduces the amount of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet and thereby improves adhesion.
• Water with an electrical conductivity of 100 ⁇ S/m or less can be produced by any method.
• the water with an electrical conductivity of 100 ⁇ S/m or less may, for example, be reverse osmosis water, ion-exchanged water, or distilled water.
• the electrical conductivity of the water used for water washing can be measured using a conductivity meter.
• any water can be used for the water washing other than the last water washing, since the above-described effect can be obtained by using water with an electrical conductivity of 100 ⁇ S/m or less for the last water washing.
• Water with an electrical conductivity of 100 ⁇ S/m or less may also be used for water washing other than the last water washing.
• water with an electrical conductivity of 100 ⁇ S/m or less is preferably used only for the last water washing, with normal water such as tap water or industrial water being used for water washing other than the last water washing.
• the electrical conductivity of the water used for the last water washing is preferably set to 50 ⁇ S/m or less, more preferably 30 ⁇ S/m or less.
• no lower limit is placed on the electrical conductivity, and the electrical conductivity may be 0 ⁇ S/m.
• the electrical conductivity is preferably set to 1 ⁇ S/m or more.
• the temperature of water used for the water washing treatment is not limited and may be any temperature. However, since excessively high temperatures place an excessive burden on the water washing equipment, the temperature of the water used for water washing is preferably set to 95 °C or lower. No lower limit is placed on the temperature of water used for water washing either, but the temperature is preferably 0 °C or higher. The temperature of the water used in the water washing may be room temperature.
• the water washing time is preferably 0.1 seconds or longer, more preferably 0.2 seconds or longer.
• No upper limit is placed on the water washing time per water washing treatment either, but in the case of production on a continuous line, the water washing time is preferably 10 seconds or less, more preferably 8 seconds or less, because a longer water washing time reduces the line speed and lowers productivity.
• Drying may optionally be performed after the water washing process.
• the drying method is not limited, and ordinary dryers or electric furnace drying methods, for example, can be applied.
• the temperature during the drying process is preferably 100 °C or lower. Within the aforementioned range, the transformation of the surface treatment coating can be suppressed. Although no lower limit is placed on the temperature, the lower limit is typically around room temperature.
• surface-treated steel sheets were produced by the following procedures, and their properties were evaluated.
• the present disclosure is not, however, limited to the following examples.
• the surface of the pretreated steel sheet with the Ni-containing layer formed thereon was treated with an aqueous solution to form a coating layer on the Ni-containing layer.
• an aqueous solution with the composition illustrated in Table 1 was used as the aqueous solution, and the coating layer was formed by performing cathodic electrolysis in the aqueous solution.
• the temperature of the aqueous solution was set to 35 °C, and the pH was adjusted to be between 3 and 5.
• the Zr coating weight and Ti coating weight were controlled by adjusting the electrical density.
• Zirconium fluoride (ZrF 4 ) was used as the Zr-containing compound and titanium fluoride (TiF 4 ) as the Ti-containing compound.
• the aqueous solution was prepared by adjusting the concentration of each ion through use of additional compounds other than the Zr-containing compound and the Ti-containing compound for the aqueous solution to have the compositions illustrated in Table 1.
• surface conditioning was performed under the set of conditions illustrated in Tables 2 and 3. Specifically, at the end of the coating formation process, the steel sheet having the aqueous solution adhering to its surface was squeezed with a wringer roll to adjust the amount of aqueous solution present on the surface of the coating layer to the amounts listed in Tables 2 and 3. The amount of aqueous solution was measured by a moisture meter using a filter-type infrared absorption method, as described above. The steel sheets were then held for the holding time illustrated in Tables 2 and 3. In other words, the aqueous solution used in the surface conditioning process is the same as that used in the aforementioned coating formation process.
• water washing treatment was applied to the steel sheets after the aforementioned surface preparation process.
• the water washing treatment was performed 1 to 5 times under the set of conditions illustrated in Tables 2 and 3.
• the method of each water washing and the electrical conductivity of the water used are illustrated in Tables 2 and 3.
• the electrical conductivity was measured using a conductivity meter.
• the coating weight of Zr oxide, the coating weight of Ti oxide, the P coating weight, and the Mn coating weight in the coating layer were measured for each of the obtained surface-treated steel sheets.
• the measurements were performed by the above-described calibration curve method using X-ray fluorescence.
• the measurement results are listed in Tables 4 and 5.
• the coating weight for Zr oxide and Ti oxide are listed as the amount of metal Zr and amount of metal Ti, respectively.
• the contact angle of ethylene glycol and the atomic ratios of adsorbed elements were measured by the following procedures for each of the obtained surface-treated steel sheets. The measurement results are listed in Tables 4 and 5.
• the contact angle of ethylene glycol on the obtained surface-treated steel sheets was measured using an automatic contact angle meter, model CA-VP, produced by Kyowa Interface Science Co., Ltd.
• the surface temperature of the surface-treated steel sheet was 20 °C ⁇ 1 °C.
• a special reagent grade ethylene glycol, produced by FUJIFILM Wako Pure Chemical Corporation, at 20 °C ⁇ 1 °C was used as the ethylene glycol.
• a 2 ⁇ l drop of ethylene glycol was dropped onto the surface of the surface-treated steel sheet, and the contact angle was measured 1 second later by the 0/2 method.
• the arithmetic mean value of the contact angles of 5 drops was used as the contact angle of the ethylene glycol.
• the contact angle was also measured after the surface-treated steel sheet was subjected to heat treatment at 200 °C for 10 minutes.
• the measurement conditions were the same as above.
• the contact angle values were substantially the same before and after heat treatment for the surface-treated steel sheets meeting the conditions of the present disclosure.
• some of the surface-treated steel sheets that did not meet the conditions of the present disclosure exhibited significant changes in contact angle values due to heat treatment.
• the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet to all elements was measured by XPS. No sputtering was performed in the measurements. From the integrated intensity of the narrow spectra of K2p, Nals, Ca2p, and Mgls at the top surface of the sample, the detected atomic ratios to all elements were quantified using the relative sensitivity factor method and calculated as (K atomic ratio + Na atomic ratio + Ca atomic ratio + Mg atomic ratio).
• the scanning X-ray photoelectron spectrometer PHI X-tool produced by ULVAC-PHI, was used, with the X-ray source being a monochrome AlK ⁇ beam, the voltage being 15 kV, the beam diameter being 100 ⁇ m ⁇ , and the take-off angle being 45°.
• BPA-free prepainted steel sheets as samples used to evaluate adhesion to a BPA-free paint were prepared according to the following procedure.
• the surface of the obtained surface-treated steel sheets was painted with a polyester-based paint for can inner surfaces (BPA-free paint) and baked at 180 °C for 10 minutes to produce BPA-free prepainted steel sheets.
• the coating weight of the paint was 60 mg/dm 2 .
• Two BPA-free prepainted steel sheets made under the same conditions were stacked so that the coated surfaces faced each other with a nylon adhesive film therebetween and were then pressure bonded under a set of conditions including a pressure of 2.94 ⁇ 10 5 Pa, a temperature of 190 °C, and a pressure bonding time of 30 seconds.
• the bonded steel sheets were then divided into 5 mm wide test pieces.
• the divided test pieces were immersed for 168 hours in a 55 °C test solution consisting of a mixed aqueous solution containing 1.5 mass% citric acid and 1.5 mass% common salt. After immersion and subsequent washing and drying, the two steel sheets of the divided test pieces were pulled apart in a tensile tester, and the tensile strength at the time of separation was measured.
• the average of three test pieces was evaluated at the following four levels. For practical purposes, a result of 1 to 3 can be evaluated as excellent adhesion to BPA-free paint.
• Table 1 Aqueous solution Composition (ppm) Zr 4+ Ti 4+ Mn 4+ PO 4 3- F NO 3 3- NH 4 + A 3000 - - - 4000 - - B 1500 - - - 2000 3000 2000 C 2000 - - 950 2000 1600 1000 D 2000 - - 950 2000 7000 2500 E 2000 2000 - 950 2000 7000 2500 F - 1500 - - 2000 3000 2000 G - 2000 - 950 2000 1600 1000 H - 2000 - 950 2000 7000 2500 I 2000 2000 2000 950 2000 7000 2500

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