Classifications

• • 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
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
• • 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
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
• • 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
• • 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
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
• • 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
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel
• • 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
  • 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
• • 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
  • C25D9/10—Electrolytic coating other than with metals with inorganic materials by cathodic processes on iron or steel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12556—Organic component
  • Y10T428/12569—Synthetic resin

Definitions

• This invention relates to chromium-chromium oxide (Cr-CrOx) coatings applied to steel substrates for packaging applications and to a method for producing said coatings.
• Tin mill products include tinplate, Electrolytic Chromium Coated Steel (ECCS, also referred to as tin free steel or TFS), and blackplate, the uncoated steel.
• Packaging steels are normally provided as tinplate, or as ECCS onto which an organic coating can be applied. In case of tinplate this organic coating is usually a lacquer, whereas in case of ECCS increasingly polymer coatings such as PET or PP are used, such as in the case of Protact ® .
• Tinplate is characterised by its excellent corrosion resistance and weldability.
• Tinplate is supplied within a range of coating weights, normally between 1.0 and 11.2 g/m 2 , which are usually applied by electrolytic deposition. At present, most tinplate is post-treated with fluids containing hexavalent chromium,
• ECCS consists of a blackplate product which has been coated with a metallic chromium layer overlaid with a film of chromium oxide, both applied by electrolytic deposition.
• ECCS excels in adhesion to organic coatings and retention of coating integrity at temperatures exceeding the melting point of tin (232°C). In those cases tinplated material cannot be used. This is important for producing polymer coated packaging steel because during the thermoplastic coating application process the steel substrate may be heated to temperatures exceeding 232°C, with the actual maximum temperature values used being dependent on the type of thermoplastic coating applied.
• thermoplastic coatings such as polypropylene (PP) or polyester terephthalate (PET) to ECCS.
• ECCS can also be supplied within a range of coating weights for both the Cr and
• ECCS CrOx coating, typically ranging between 20 - 110 and 2 - 20 mg/m 2 respectively.
• ECCS can be delivered with equal coating specification for both sides of the steel strip, or with different coating weights per side, the latter being referred to as differentially coated strip.
• the production of ECCS currently involves the use of solutions on the basis of chromium in its hexavalent state, also known as hexavalent chromium or Cr(VI).
• Hexavalent chromium is nowadays considered a hazardous substance that is potentially harmful to the environment and constitutes a risk in terms of worker safety. There is therefore an incentive to develop alternative metal coatings that are able to replace conventional tinplate and ECCS, without the need to resort to the use of hexavalent chromium during manufacturing.
• a chromium metal - chromium oxide (Cr-CrOx) coating layer produced in a single plating step by using a trivalent chromium electroplating process.
• the packaging steel substrate is preferably provided in the form of a strip.
• the two-step vertical process uses a sulphuric acid free Cr(VI) electrolyte for applying the chrome oxide layer in the second step.
• Sulphuric acid is needed for a good efficiency in applying chrome metal and is therefore always used for the chrome metal plating step in these processes.
• the "one step vertical” and the “one step horizontal high current density (HCD) process” always have sulphate in the oxide layer because the chromium metal and chromium oxide are produced simultaneously in the same electrolyte (Boelen, thesis TU Delft 2009, page 8-9, ISBN 978-90-805661-5-6). In all cases the
• ECCS consists of a chromium oxide layer on top of the chromium metal.
• a coating layer comprising chromium metal and chromium oxide is deposited, and not by first depositing a chromium metal layer, and then providing a chromium oxide layer on top as a conversion layer.
• the Cr-CrOx layer should consist of a mixture of Cr-oxide and Cr-metal and the Cr-oxide should not be present as a distinct layer on the outermost surface, but mixed through the whole layer Cr-CrOx.
• the phrase single plating step is therefore not limited to mean that only one of these single plating steps is used.
• the packaging steel substrate is usually provided in the form of a strip of low carbon (LC), extra low carbon (ELC) or ultra low carbon (ULC) with a carbon content, expressed as weight percent, of between 0.05 and 0.15 (LC), between 0.02 and 0.05 (ELC) or below 0.02 (ULC) respectively. Alloying elements like manganese, aluminium, nitrogen, but sometimes also elements like boron, are added to improve the mechanical properties (see also e.g. EN 10 202, 10 205 and 10 239).
• the substrate consists of an interstitial-free low, extra-low or ultra-low carbon steel, such as a titanium stabilised, niobium stabilised or titanium-niobium stabilised interstitial-free steel.
• a chromium metal - chromium oxide (Cr-CrOx) coating produced from a trivalent chromium based electroplating process provides excellent adhesion to organic coatings.
• the chromium metal - chromium oxide (Cr-CrOx) coating produced from a trivalent chromium electrodeposition process has very similar adhesion properties compared to conventional ECCS produced via a hexavalent chromium electrodeposition process. By increasing the thickness of the Cr-CrOx coating layer the porosity of the coating is reduced and its corrosion resistance properties improve.
• the Cr-CrOx coating can be applied onto conventional, non-passivated, electrolytic, and optionally flowmelted, tinplate (ETP, Electrolytic Tinplate).
• ETP Electrolytic Tinplate
• the Cr-CrOx layer ensures that the growth of tin oxides is suppressed, i.e. it has a passivation function.
• the wet adhesion performance i.e. the organic coating adhesion after sterilisation, outperforms conventional hexavalent chromium passivated tinplate.
• the resistance to so-called sulphur staining i.e.
• the brown discolouration of tinplate due to contact with sulphur containing fill-goods can be fully suppressed by applying a sufficiently thick Cr-CrOx coating.
• the material according to the invention is therefore very suitable for replacement of hexavalent chromium passivated tinplate, optionally exceeding the technical performance limits of standard tinplate. From a process point of view, the fact that the Cr-CrOx coating layer is applied in a single process step means that two process steps are combined, which is beneficial in terms of process economy and in terms of environmental impact.
• the Cr-CrOx coating can also be applied directly onto the
• blackplate packaging steel substrate without prior application of a tin coating, i.e. directly applied onto the bare steel surface.
• a tin coating i.e. directly applied onto the bare steel surface.
• Merriam Webster blackplate is defined as sheet steel that has not yet been made into tin plate by being coated with tin or that is used uncoated where the protection afforded by tin is unnecessary. It was found that the dry adhesion levels to organic coatings for both thermoset lacquers and thermoplastic coatings, of this material can approach those normally associated with the use of ECCS.
• the material according to the invention can be used to directly replace ECCS for applications that require a moderate corrosion resistance.
• the Cr-CrOx coating layer applied onto non-passivated tinplate contains at least 20 mg Cr/m 2 , to create a tin oxide passivating effect. This thickness is adequate for many purposes.
• the Cr-CrOx coating layer applied onto non-passivated tinplate contains at least 40 mg Cr/m 2 , preferably at least 60 Cr/m 2 , to create a tin oxide passivating effect and to prevent or eliminate sulphur staining.
• a layer of 20 mg Cr/m 2 was found to be too thin. Starting at thicknesses of about 40 mg Cr/m 2 the sulphur staining is already much reduced, whereas at a layer thickness of of at least about 60 mg Cr/m 2 sulphur staining is practically eliminated.
• a suitable maximum thickness was found to be 140 mg Cr/m 2 .
• the maximum thickness was found to be 140 mg Cr/m 2 .
• Cr-CrOx coating layer applied onto non-passivated tinplate contains at least 20 to 140 mg Cr/m 2 , more preferably at least 40 and/or at most 90 mg Cr/m 2 , and most preferably at least 60 and/or at most 80 mg Cr/m 2 .
• the major advantage besides the elimination of hexavalent chromium from manufacturing is the potential to create a product with superior sulphur staining resistance and improved corrosion resistance.
• the Cr-CrOx coating layer applied onto blackplate is at least
• the Cr-CrOx coating layer applied onto blackplate is at least 40 and more preferably at least 60 mg Cr/m 2 .
• a suitable maximum thickness was found to be 140 mg Cr/m 2 .
• the Cr-CrOx coating layer applied onto blackplate contains at least 20 to 140 mg Cr/m 2 , more preferably at least 40 mg Cr/m2, and most preferably at least 60 mg Cr/m 2 . In an embodiment a suitable maximum is 110 mg Cr/m 2 .
• the Cr-CrOx coated blackplate aims to replace ECCS.
• the major advantage besides the elimination of hexavalent chromium from manufacturing is the potential to create a product for applications for which the superior corrosion resistance properties of tinplate are not required.
• the fact that the Cr-CrOx coating layer is applied in a single process step means that two process steps are combined, which is beneficial in terms of process economy and in terms of environmental impact.
• the Cr-CrOx coating can also be applied to a cold-rolled and recovery annealed blackplate, or to a cold-rolled and recovery annealed electrolytic, and optionally flowmelted, tinplate. These substrates have a recovery annealed substrate, rather than the recystallised single reduced ETP or blackplate or the double reduced blackplate. The difference in microstructure of the substrate was not found to materially affect the Cr-CrOx coating.
• thermoplastic coatings can be used in combination with thermoplastic coatings, but also for applications where traditionally ECCS is used in combination with lacquers (i.e. for bakeware such as baking tins, or products with moderate corrosion resistance requirements) or as a substitute for conventional tinplate for applications where requirements in terms of corrosion resistance are moderate.
• lacquers i.e. for bakeware such as baking tins, or products with moderate corrosion resistance requirements
• the coated substrate is further provided with an organic coating, consisting of either a thermoset organic coating, or a thermoplastic single layer polymer coating, or a thermoplastic multi-layer polymer coating.
• the Cr-CrOx layer provides excellent adhesion to the organic coating similar to that achieved by using conventional ECCS.
• thermoplastic polymer coating is a polymer coating system comprising one or more layers comprising the use of thermoplastic resins such as polyesters or polyolefins, but can also include acrylic resins, polyamides, polyvinyl chloride, fluorocarbon resins, polycarbonates, styrene type resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalised polymers.
• thermoplastic resins such as polyesters or polyolefins, but can also include acrylic resins, polyamides, polyvinyl chloride, fluorocarbon resins, polycarbonates, styrene type resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalised polymers.
• Polyester is a polymer composed of dicarboxylic acid and glycol.
• suitable dicarboxylic acids include therephthalic acid, isophthalic acid, naphthalene dicarboxylic acid and cyclohexane dicarboxylic acid.
• suitable glycols include ethylene glycol, propane diol, butane diol, hexane diol, cyclohexane diol, cyclohexane dimethanol, neopentyl glycol etc. More than two kinds of dicarboxylic acid or glycol may be used together.
• Polyolefins include for example polymers or copolymers of ethylene, propylene,
• Acrylic resins include for example polymers or copolymers of acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester or acrylamide.
• Polyamide resins include for example so-called Nylon 6, Nylon 66, Nylon 46,
• Polyvinyl chloride includes homopolymers and copolymers, for example with ethylene or vinyl acetate.
• Fluorocarbon resins include for example tetrafluorinated polyethylene, trifluorinated monochlorinated polyethylene, hexafluorinated ethylene- propylene resin, polyvinyl fluoride and polyvinylidene fluoride.
• Functionalised polymers for instance by maleic anhydride grafting include for example modified polyethylenes, modified polypropylenes, modified ethylene acrylate copolymers and modified ethylene vinyl acetates.
• thermoplastic polymer coating systems have shown to provide excellent performance in can-making and use of the can, such as shelf-life.
• the invention is embodied in a process for producing a coated steel substrate for packaging applications, the process comprising the electro-deposition of a chromium metal - chromium oxide coating on the substrate with the electrolytic deposition on said substrate of said chromium metal - chromium oxide coating occurring in a single plating step from a plating solution comprising a trivalent chromium compound, an optional chelating agent, an optional conductivity enhancing salt, an optional depolarizer, an optional surfactant and to which an acid or base can be added to adjust the pH.
• the electro-deposition of the Cr-CrOx coating is achieved by using an electrolyte in which the chelating agent comprises a formic acid anion, the conductivity enhancing salt contains an alkali metal cation and the depolarizer comprises a bromide containing salt.
• the cationic species in the chelating agent, the conductivity enhancing salt and the depolarizer is potassium.
• the benefit of using potassium is that its presence in the electrolyte greatly enhances the electrical conductivity of the solution, more than any other alkali metal cation, thus delivering a maximum contribution to lowering of the cell voltage required to drive the electro-deposition process.
• the composition of the electrolyte used for the Cr-CrOx deposition was: 120 g/l basic chromium sulphate, 250 g/l potassium chloride, 15 g/l potassium bromide and 51.2 g/l potassium formate.
• the pH was adjusted to values between 2.3 and 2.8 measured at 25°C by the addition of sulphuric acid.
• the chromium containing coating is preferably deposited from the trivalent chromium based electrolyte at a bath temperature of between 40 and 70°C, preferably of at least 45°C and/or at most 60°C.
• the Cr-layer consists of a mixture of Cr-oxide and Cr-metal and that the Cr-oxide is not present as a distinct layer on the outermost surface, but is mixed through the whole layer. This is also indicated by the O-peak that is present in the whole Cr-layer. In all cases the Cr-CrOx layer has a shiny metallic appearance.
• the formation of Cr(IV) can be prevented by using one, more or only hydrogen gas diffusion anodes at which hydrogen gas (H 2 (g)) is oxidised.
• H + protons
• H 3 0 + hydronium ions
• the oxidation of H 2 (g) to H + (aq) prevents the occurrence of undesirable oxidation reactions, such as the formation of Cr(IV), which occur at a higher anodic overpotential when using an anode at which water (H 2 0) is oxidised to oxygen (0 2 (g)).
• H 2 (g) is oxidised at the gas diffusion anode to
• the electrode potential is measured against the standard hydrogen electrode.
• the standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials.
• the anode operating (non-zero current) potential needed to generate a specific anodic current is determined by the activation overpotential (i.e. the potential difference required for driving the electrode reaction) and the concentration overpotential (i.e. the potential difference required to compensate for concentration gradients of electro-active species at the electrode).
• no depolariser is added to the electrolyte.
• a hydrogen gas diffusion anode is used then the addition of a depolariser to the electrolyte is no longer needed.
• the use of a hydrogen gas diffusion anode has the added advantage that the use of a chloride containing electrolyte becomes possible without the risk of chlorine formation. This chlorine gas is potentially harmful to the environment and to the workers and is therefore undesirable. This means that in the case of a Cr(III) electrolyte the electrolyte could be partly or entirely based on chlorides.
• the advantage of using a chloride based electrolyte is that the conductivity of the electrolyte is much higher compared to a sulphate only based electrolyte, which leads to a lower cell voltage that is required to run the electrodeposition, which results in a lower energy consumption.
• a hydrogen gas diffusion anode is a porous anode containing a three-phase interface of hydrogen gas, the electrolyte fluid and a solid electrocatalyst (e.g. platinum) that has been applied to the electrically conducting porous matrix (e.g. porous carbon or a porous metal foam).
• the main advantage of using such a porous electrode is that it provides a very large internal surface area for reaction contained in a small volume combined with a greatly reduced diffusion path length from the gas-liquid interface to the reactive sites.
• This design the mass transfer rate of hydrogen is greatly enhanced, while the true local current density is reduced at a given overall electrode current density, resulting in a lower electrode potential.
• a gas diffusion anode assembly to be used in the proposed electrodeposition method typically comprises the use of the following functional components (see Fig . 5) : a gas feeding chamber 1, a current collector 2 and a gas diffusion anode, which consists of an hydrophobic porous gas diffusion transport layer 3 combined with an hydrophilic reaction layer 4 (see Fig. 5).
• the latter is made up of a network of micropores that are (partly) drowned with liquid electrolyte.
• the reaction layer is provided with a proton exchange membrane on the outside 5, like a Nafion ® membrane, to prevent the diffusion of chemical species (like anions or large neutral molecules) present in the bulk liquid electrolyte inside the gas diffusion anode, as these compounds can potentially poison the electrocatalyst sites, causing degradation in electrocatalytic activity.
• a proton exchange membrane on the outside 5, like a Nafion ® membrane, to prevent the diffusion of chemical species (like anions or large neutral molecules) present in the bulk liquid electrolyte inside the gas diffusion anode, as these compounds can potentially poison the electrocatalyst sites, causing degradation in electrocatalytic activity.
• the main function of the gas feeding chamber is to supply hydrogen gas evenly to the hydrophobic backside of the hydrogen gas diffusion anode.
• the gas feeding chamber needs two connections: one to feed hydrogen gas and one to enable purging of a small amount of hydrogen gas to prevent the build-up of gas phase contaminations potentially present in trace amounts in the hydrogen gas supplied.
• the gas feeding chamber often contains a channel type structure to ensure that hydrogen gas is distributed evenly over the hydrophobic backside.
• the electrical current collector 2 is (usually) attached to the hydrophobic backside 3 of the hydrogen gas diffusion anode to enable the transport of the electrical current generated inside the anode to a rectifier (not shown in Fig. 5).
• This current collector plate must be designed in such a way to enable the hydrogen gas to contact the backside of the hydrogen gas diffusion anode so it can be transported to the reactive side inside the gas diffusion anode. Usually this is accomplished by using an electrically conductive plate with a large number of holes, a mesh or an expanded metal sheet made from e.g. titanium.
• gas feeding channels and electrical current collector can also be combined into a single component, which is then pressed against the hydrophobic back-side of the gas diffusion anode.
• the hydrogen gas diffuses through the hydrophobic backside of the hydrogen gas diffusion anode it comes into contact with the electrolyte, which is present in the hydrophilic part of the anode, i.e. the reaction layer (see Fig. 5, right hand side).
• the hydrogen gas dissolves into the electrolyte and is transported by diffusion to the electrocatalytic active sites of the hydrogen gas diffusion anode.
• platinum is used as electrocatalyst, but also other materials like platinum- ruthenium or platinum-molybdenum alloys can be used.
• the dissolved hydrogen is oxidised : the electrons that are generated are transported through the conductive matrix of the gas diffusion anode (usually a carbon matrix) to the current collector 2, while the hydronium ions (H + ) diffuse through the proton exchange membrane into the electrolyte.
• the coated substrate is further provided on one or both sides with an organic coating, consisting of a thermosetting organic coating by a lacquering step, or a thermoplastic single layer, or a thermoplastic multi-layer polymer by a film lamination step or a direct extrusion step.
• an organic coating consisting of a thermosetting organic coating by a lacquering step, or a thermoplastic single layer, or a thermoplastic multi-layer polymer by a film lamination step or a direct extrusion step.
• thermoplastic polymer coating is a polymer coating system comprising one or more layers comprising the use of thermoplastic resins such as polyesters or polyolefins, but can also include acrylic resins, polyamides, polyvinyl chloride, fluorocarbon resins, polycarbonates, styrene type resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalised polymers; and/or copolymers thereof; and/or blends thereof.
• thermoplastic resins such as polyesters or polyolefins, but can also include acrylic resins, polyamides, polyvinyl chloride, fluorocarbon resins, polycarbonates, styrene type resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalised polymers; and/or copolymers thereof; and/or blends thereof.
• the substrate is cleaned prior to Cr-CrOx electrodeposition by dipping the substrate in a sodium carbonate solution containing between 1 to 50 g/l of Na 2 C0 3 at a temperature of between 35 and 65°C, and wherein the cathodic current density of between 0.5 and 2 A/dm 2 is applied for a period of between 0.5 and 5 seconds.
• the sodium carbonate solution containing at least 2 and/or at most 5 g/l of Na 2 C0 3 .
• Example 1 Sheets of conventional, non-passivated, flow melted tinplate
• the samples were dipped into a trivalent chromium electrolyte kept at 50°C composed of: 120 g/l of basic chromium sulphate, 250 g/l of potassium chloride, 15 g/l of potassium bromide and 51.2 g/l of potassium formate.
• the pH of this solution was adjusted to 2.3 measured at 25°C by adding sulphuric acid .
• a Cr-CrOx coating containing between 21 - 25 mg Cr/m 2 was deposited on the surface by applying a cathodic current density of 10 A/dm 2 for approximately 1 second, using a platinised titanium anode as counter electrode. The samples so produced showed a shiny metallic appearance.
• the tin oxide layer is reduced by a controlled small cathodic current in a 0.1% solution of hydrobromic acid (HBr) that is freed from oxygen by scrubbing with nitrogen.
• HBr hydrobromic acid
• the progress of the reduction of the oxide is followed by potential measurement and the charge passed for the complete reduction (expressed as Coulomb/m 2 or C/m 2 ) serves as a measure of the tin oxide layer thickness.
• the results for the sample according to Example 1 are presented in Table 1, including the performance of the reference material, which is the same tinplate material that was passivated using hexavalent chromium, i.e. so-called 311 passivated tinplate.
• Example 2 Sheets of conventional, non-passivated, flow melted tinplate
• the tinplate variant manufactured according to the invention performed consistently equal or better compared to the standard tinplate that is passivated using hexavalent chromium (i.e. the reference). Striking is the fact that no sulphur staining was found for the material according to the invention, which is difficult to achieve with conventional passivated tinplate and notoriously difficult to achieve with alternative passivations for tinplate that are free of hexavalent chromium.
• Example 3 A coil of blackplate (common steel grade and temper), not containing any metal coating, was treated in a processing line running at a line speed of 20 m/min.
• the processing sequence started with alkaline cleaning of the steel by running the strip for approximately 10 seconds through a solution containing 30 ml/1 of a commercial cleaner (Percy P3) and 40 g/l of NaOH, which was kept at 60 °C. During cleaning of the strip an anodic current density of 1.3 A/dm 2 was applied. After rinsing with de-ionised water, the steel strip was passed through an acid solution for approximately 10 seconds, to activate the surface.
• the acid solution consisted of 50 g/l H 2 S0 4 , which was kept at 25
• the steel strip was passed into an electroplating tank containing the trivalent chromium based electrolyte kept at 50°C.
• This electrolyte consisted of: 120 g/l of basic chromium sulphate, 250 g/l of potassium chloride, 15 g/l of potassium bromide and 51.2 g/l of potassium formate.
• the pH of this solution was adjusted to 2.3 measured at 25 °C by adding sulphuric acid.
• the electroplating tank contained a set of anodes consisting of platinised titanium.
• the material so produced was passed through a coating line to apply a commercially available 20 micrometer thick PET film, through heat sealing. After film lamination, the coated strip was post-heated to temperatures above the melting point of PET, and subsequently quenched in water at room temperature, as per a usual processing method for the PET lamination of metals. The same procedure was followed for the manufacturing of reference material, using a commercially produced coil of ECCS.
• the DRD cans were subsequently filled with different media, closed and exposed to a sterilisation treatment. Some cans were processed that contained a scratch made on the can wall, to simulate and observe the effect of incidental coating damage. An overview of the type of sterilisation tests done is presented in Table 4.
• the performance ranking is on a scale from 0 to 5, with 0 being an excellent performance and 5 a very bad performance.
• Example 4 A coil of blackplate (common steel grade and temper), not containing any metal coating, was treated in a processing line identical to that described in the previous example to apply a Cr-CrOx coating.
• Fig. 1 and 2 show typical SEM images, which show the deposition of very fine grains of chromium metal-chromium oxide onto the surface.
• Figure 1 relates to a tinplate substrate and figure 2 relates to a blackplate substrate.
• Figure 3 shows an overview of various packaging applications. On the X-axis are packaging steel grades, and on the Y-axis a typical thickness range is shown for these applications for which the packaging steel substrate according to the invention could be used.
• Figure 4 shows where the current is plotted against the anode potential in SHE and Figure 5 shows a schematic drawing of a gas diffusion anode.

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• 2013
  • 2013-11-21 JP JP2015543421A patent/JP6407880B2/ja active Active
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