Chromium-chromium oxide coatings applied to steel substrates for packaging applications and a method for producing said coatings

Abstract

A coated steel substrate for packaging applications, the substrate containing (1) a recrystallisation annealed single or double reduced packaging steel blackplate, or (2) a cold-rolled and recovery annealed blackplate, wherein one or both sides of the substrate is coated with a chromium metal-chromium oxide coating layer produced in a single process step by using a trivalent chromium electroplating process. A process for obtaining the coated steel substrate.

1 . A process for producing a coated steel substrate for packaging applications by depositing a chromium metal-chromium oxide coating on the substrate for packaging applications containing
 (a) a recrystallisation annealed single or double reduced packaging steel blackplate, or   (b) a cold-rolled and recovery annealed blackplate,   
       comprising electrolytically depositing on said substrate said chromium metal-chromium oxide coating in a single process step from a plating solution comprising a mixture of a trivalent chromium compound, a chelating agent, an optional conductivity enhancing salt, an optional depolarizer, an optional surfactant, to which an acid or base is optionally added to adjust the pH, wherein the plating solution does not contain a buffering agent, and wherein a sufficiently high cathodic current density is being applied to deposit chromium metal. 
     
     
         2 . The process according to  claim 1 , wherein 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. 
     
     
         3 . The process according to  claim 1 , wherein the chelating agent, the conductivity enhancing salt and the depolarizer contain a cationic species and the cationic species in the chelating agent, the conductivity enhancing salt and the depolarizer is potassium. 
     
     
         4 . The process according to  claim 1 , wherein the electrolytic depositing on said substrate said chromium metal-chromium oxide coating deposits a chromium metal-chromium oxide layer on the blackplate containing a total chromium content of at least 20 mg/m 2 . 
     
     
         5 . The process according to  claim 1 , wherein the electrolytic depositing on said substrate said chromium metal-chromium oxide coating deposits a chromium metal-chromium oxide layer on the blackplate containing a total chromium content of at most 140 mg/m 2 . 
     
     
         6 . The process according to  claim 1 , wherein 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. 
     
     
         7 . The process according to  claim 1 , wherein an anode is chosen that reduces or eliminates the oxidation of Cr(III) ions to Cr(VI) ions during the plating step. 
     
     
         8 . A coated steel substrate for packaging applications containing
 (a) a recrystallisation annealed single or double reduced packaging steel blackplate, or   (b) a cold-rolled and recovery annealed blackplate,   
       wherein one or both sides of the substrate is coated with a chromium metal-chromium oxide coating layer produced in a single process step by using a trivalent chromium electroplating process, wherein the coated substrate is further provided with an organic coating, consisting of a thermoplastic single-layer polymer coating or thermoplastic multi-layer polymer coating. 
     
     
         9 . The coated substrate for packaging applications according to  claim 8 , wherein the chromium metal-chromium oxide layer contains a total chromium content of at least 20 mg/m 2 . 
     
     
         10 . The coated substrate for packaging applications according to  claim 8 , wherein the chromium metal-chromium oxide layer contains a total chromium content of at most 140 mg/m 2 . 
     
     
         11 . The coated substrate for packaging applications according to  claim 8 , wherein the organic coating consists of the thermoplastic single or multi-layer polymer coating, wherein the thermoplastic polymer of the thermoplastic single or multi-layer polymer coating is a polymer coating system comprising one or more layers comprising polyester and/or copolymers thereof and/or blends thereof. 
     
     
         12 . The process according to  claim 1 , wherein the electrolytic deposition deposits a chromium metal-chromium oxide layer on the blackplate containing a total chromium content of at least 40 mg/m 2 . 
     
     
         13 . The process according to  claim 1 , wherein the electrolytic deposition deposits a chromium metal-chromium oxide layer on the blackplate containing a total chromium content of at least 60 mg/m 2 . 
     
     
         14 . The process according to  claim 1 , wherein the electrolytic deposition deposits a chromium metal-chromium oxide layer on the blackplate containing a total chromium content of at most 110 mg/m2. 
     
     
         15 . The coated substrate for packaging applications according to  claim 8 , wherein the chromium metal-chromium oxide layer contains a total chromium content of at least 40 mg/m 2 . 
     
     
         16 . The coated substrate for packaging applications according to  claim 8 , wherein the chromium metal-chromium oxide layer contains a total chromium content of at least 60 mg/m 2 . 
     
     
         17 . The coated substrate for packaging applications according to  claim 8 , wherein the chromium metal-chromium oxide layer contains a total chromium content of at most 110 mg/m 2 . 
     
     
         18 . The process according to  claim 1 , wherein 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, wherein the thermoplastic single layer or thermoplastic multi-layer polymer coating is a polymer coating system comprising one or more layers comprising a thermoplastic resin selected from the group consisting of polyesters, polyolefins, 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. 
     
     
         19 . The process according to  claim 1 , wherein a gas diffusion anode is chosen that reduces or eliminates the oxidation of Cr(III) ions to Cr(VI) ions during the plating step, such as a anode. 
     
     
         20 . The process according to  claim 8 , wherein the thermoplastic multi-layer polymer coating is a polymer coating system comprising one or more layers comprising thermoplastic resins selected from the group consisting of polyesters or polyolefins, 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.