JP2016501985A - Chromium-chromium oxide coating applied to steel substrates for packaging applications and method for producing said coating - Google Patents

Abstract

The present invention is characterized in that one or both sides are coated with a metal chromium-chromium oxide coating layer produced by using a trivalent chromium electroplating process in a single process step, i) Conventional Non-passivated, electrodeposited, optionally fluid melted tinplate, or ii) cold rolled, recovery annealed, electrodeposited, optionally fluid melted tinplate containing packaging applications TECHNICAL FIELD The present invention relates to a coated steel substrate for the purpose of obtaining a coated steel substrate.

Description

  The present invention relates to a chromium-chromium oxide coating applied to a steel substrate for packaging applications and a method for producing said coating.

  Tin factory products include tinplate, electrolytic chrome coated steel (also referred to as ECCS, Wuxi Steel or TFS), tinplate, and uncoated steel. Packaging steel is usually provided as tinplate to which an organic coating can be applied, or as ECCS. In the case of tinplate, this organic coating is usually a lacquer, whereas in the case of ECCS, the use of polymer coatings such as PET or PP is increasing, as in the case of Protact®. .

Tinplate is characterized by its excellent corrosion resistance and weldability. Tin is supplied in the range of coating weight of usually between 1.0 g / ^{m 2} and 11.2 g / ^{m 2,} it is usually applied by electrodeposition. At present, most tinplates are post-treated with fluids containing hexavalent chromium Cr (VI) using immersion or electrically assisted application processes. The aim of this post-treatment is to passivate the tin surface in order to stop or reduce the growth of tin oxide, because the oxide layer that is too thick will eventually result in an organic coating such as lacquer. This is because it may cause problems with respect to adhesion. It is important that the passivation treatment not only suppresses or eliminates tin oxide growth, but can also maintain or improve the adhesion level of the organic coating. The passivated outer surface of the tin is extremely thin (less than 1 micron thick) and consists of a mixture of tin oxide and chromium oxide.

ECCS consists of a tin plate that is coated with a metallic chromium layer (both applied by electrodeposition) overlaid with a chromium oxide film. ECCS excels in adhesion to organic coatings and maintaining coating integrity at temperatures above the melting point of tin (232 ° C.). In these cases, plated material cannot be used. This is important for producing polymer coated packaging steel because the steel substrate may be heated to temperatures above 232 ° C. during the thermoplastic coating application process. And the maximum temperature value actually used depends on the type of thermoplastic coating applied. This heating cycle is necessary to allow initial heat sealing / bonding (preheat treatment) to the plastic substrate and is often followed by post heat treatment to modify the polymer properties. The chromium oxide layer is believed to be responsible for the excellent adhesion of thermoplastic coatings such as polypropylene (PP) or polyester terephthalate (PET) to ECCS. ECCS is also the coating of both Cr and CrOx, typically, each of which can be supplied with a coating weight in the range of between 20~110mg / ^{m 2} and 2 to 20 mg / ^{m 2.} The ECCS can be delivered with equal coating specifications on both sides of the steel strip or with different coating weights on each side, the latter being said to coat the steel strip differently. The manufacture of ECCS currently involves using a solution in its hexavalent state, also known as hexavalent chromium or Cr (VI), as the main component of chromium.

  Hexavalent chromium is currently considered a hazardous substance that is potentially harmful to the environment and is considered dangerous for worker safety. Therefore, there is a motivation for the development of alternative metal coatings that can replace conventional tinplate and ECCS without relying on the use of hexavalent chromium during fabrication.

  It is an object of the present invention to provide an alternative to the use of hexavalent chromium to passivate tin.

  It is an object of the present invention to provide an alternative to conventional tinplate to improve product properties, for example with respect to corrosion performance and resistance to sulfur coloring.

  It is also an object of the present invention to provide a substrate that replaces tinplate and ECCS that provides excellent dry adhesion to organic coatings combined with corrosion protection that does not rely on the use of hexavalent chromium during fabrication.

One or more of these purposes are
1. 1. conventional non-passivated electrodeposited, optionally fluid melted tinplate (ie ETP), or Manufactured in a single plating step, using cold-rolled, recovery-annealed, electrodeposited, optionally fluid-melted tinplate, using trivalent chromium electroplating on one or both sides of the substrate It is achieved by providing a steel substrate for packaging coated with a coated metal chromium-chromium oxide (Cr-CrOx) coating layer.

  The packaging steel substrate is preferably provided in the form of a strip.

  Three types of chrome plating methods are commonly used throughout the world for the manufacture of ECCS. The three methods are “one-step vertical method” (V-1), “two-step vertical method” (V-2), and “one-step horizontal high current density method” (HCD), and Cr (VI ) Based on electrolyte. The specification of ECCS is standardized by European electrical standard EN10202: 2001. In the two-step vertical method, a Cr (VI) electrolyte without sulfuric acid is used to apply the chromium oxide layer in the second step. Sulfuric acid is required for superior effectiveness in metallic chromium applications and is therefore always used for the metallic chromium plating step in these processes. "One-step vertical method" and "One-step horizontal high current density (HCD) method" always have sulfate in the oxide layer, because metal chromium and chromium oxide are produced simultaneously in the same electrolyte. (Boelen, Doctoral Dissertation TU Delft 2009, 8-9, ISBN 978-90-8056661-5-6). In all cases, ECCS consists of a chromium oxide layer on metallic chromium.

  In the method according to the present invention, rather than first depositing a chromium metal layer and then providing a chromium oxide layer on top as a conversion layer, a coating layer comprising chromium metal and chromium oxide is deposited. The Cr—CrOx layer should consist of a mixture of Cr oxide and Cr metal, and the Cr oxide is not mixed as a separate layer on the outermost surface but is mixed throughout the Cr—CrOx layer. Should. Of course, there may be two or more of these single plating steps one after the other if a thicker coating layer including, for example, a metallic chromium and chromium oxide layer is to be deposited. Therefore, the phrase single plating step does not necessarily mean that only one of these single plating steps is used.

  The packaging steel substrate has a weight percent of carbon content between 0.05 and 0.15 (LC), between 0.02 and 0.05 (ELC) or less than 0.02 (ULC), respectively. Are typically provided in the form of low carbon (LC), ultra low carbon (ELC) or ultra low carbon (ULC) strips represented by Elements that become alloys such as manganese, aluminum, nitrogen, and sometimes elements such as boron are also added to improve mechanical properties (see also, eg, EN 10202, 10205, and 10239). In one embodiment of the present invention, the substrate may be a low carbon steel, ultra low carbon steel, or ultra low carbon, such as titanium stabilized, niobium stabilized, or titanium-niobium stabilized steel without intercalation. Made of carbon steel.

  Metal chromium-chromium oxide (Cr-CrOx) coatings made from trivalent chromium based on an electroplating process have been found to exhibit excellent adhesion to organic coatings. In this embodiment, the metal chromium-chromium oxide (Cr-CrOx) coating produced from the trivalent chromium electrodeposition process has very similar adhesion compared to conventional ECCS produced by the hexavalent chromium electrodeposition process. Have By increasing the thickness of the Cr—CrOx coating layer, the porosity of the coating is reduced and its corrosion resistance is improved.

  The Cr-CrOx coating can be applied to conventional, non-passivated electrodeposited and optionally fluid melted tin (ETP, electrolytic tin). The Cr-CrOx layer ensures that the growth of tin oxide is suppressed, i.e. it has a passivating function. It was unexpectedly found that as the Cr-CrOx thickness increases, the wet adhesion performance, i.e., organic coating adhesion after sterilization, outperforms conventional hexavalent chromium passivated tinplate. In addition, so-called sulfur coloring, i.e. brown discoloration of the tin based on contact with sulfur-containing contents, can be completely suppressed by applying a sufficiently thick Cr-CrOx coating. Therefore, the material according to the invention is very suitable for replacing hexavalent chromium passivated tin plates and in some cases exceeds the technical performance limits of standard tin plates. From a process point of view, the fact that the Cr—CrOx coating layer is applied in a single process step means that the two process steps are combined, which is advantageous with respect to process economics and environmental impact. It is.

  Alternatively, the Cr—CrOx coating can be applied directly to the tinplate packaging steel substrate without prior application of the tin coating, ie directly to the bare steel surface. According to Merriam Webster, a tin plate is defined as a steel plate that has never been tin-plated by being coated with tin, or a steel plate that is used uncoated that does not require the protection afforded by tin. It has been found that the dry adhesion level of this material to organic coatings, both thermoset lacquers and thermoplastic coatings, can be approximately equal to that normally associated with the use of ECCS. The material according to the present invention can be used to directly replace ECCS for applications that require moderate corrosion resistance.

  Its great advantage is that, in terms of both environmental impact and health and safety, the present invention prevents the use of hexavalent chromium chemistry while retaining the performance properties of products normally attributed to ECCS and tinplate. It is a fact.

In one embodiment, the Cr—CrOx coating layer applied to the unpassivated tin contains at least 20 mg Cr / m ² and creates a tin oxide passivating effect. This thickness is appropriate for many purposes.

In one embodiment, the Cr—CrOx coating layer applied to the unpassivated tin contains at least 40 mg Cr / m ² , preferably at least 60 Cr / m ² to create a tin oxide passivating effect, Prevent or eliminate sulfur discoloration. To prevent or eliminate sulfur discoloration, the 20 mg Cr / m ² layer was found to be too thin. Although sulfur discoloration is practically eliminated with a layer thickness of at least about 60 mg Cr / m ² , starting with a thickness of about 40 mg Cr / m ² , the sulfur discoloration is already greatly reduced.

A suitable maximum thickness was found to be 140 mg Cr / m ² . Preferably, the Cr—CrOx coating layer applied to the non-passivated tin is 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 contains at most 80 mg Cr / m ² .

  In these embodiments, the goal is to replace the tinplate passivated with hexavalent chromium. A major advantage added to eliminating hexavalent chromium from fabrication is the potential to create products with extremely good resistance to sulfur discoloration and improved corrosion resistance.

  It has been found that the color of the material change with increasing product Cr—CrOx layer thickness becomes darker (ie, lower L-value) as the coating thickness increases. Since the optical properties of packaging steel are very important to create the attractive and aesthetic appearance of metal containers such as aerosol cans, this can also be considered a disadvantage of the present invention for certain applications. it can. However, one way to avoid these problems is to use, for example, a differential coating that uses a low Cr—CrOx coating weight on one side of the material while applying a thicker Cr—CrOx coating weight on the other side. That would be true. A surface containing a thicker Cr—CrOx coating weight should be used inside the container in order to use the benefits of improved corrosion resistance properties. In that case, the surface with the lower Cr—CrOx coating weight is on the outside of the container, where the need for corrosion resistance is usually less important, ensuring optimal optical properties.

In one embodiment, the Cr—CrOx coating layer applied to the tinplate is at least 20 mg Cr / m ² and has excellent adhesion to organic coatings combined with ECCS functionality (eg, moderate corrosion resistance). ) Is created. Preferably the Cr—CrOx coating layer applied to the tin plate is at least 40 mg Cr / m ² , more preferably at least 60 mg Cr / m ² . A suitable maximum thickness was found to be 140 mg Cr / m ² . Preferably, the Cr—CrOx coating layer applied to the tin plate contains at least 20 to 140 mg Cr / m ² , more preferably at least 40 mg Cr / m ² , and most preferably at least 60 mg Cr / m ² . In one embodiment, a suitable maximum is 110 mg Cr / m ² .

  The Cr-CrOx coated tin plate aims to replace ECCS. A major advantage of eliminating hexavalent chromium from fabrication is the potential to create products for applications where the very good corrosion resistance properties of tinplate are not required. From a process point of view, the fact that the Cr—CrOx coating layer is applied in a single process step means that the two process steps are combined, which is beneficial in terms of process economics and environmental impact. It is.

  The Cr-CrOx coating can also be applied to cold rolled and recovery annealed tin plate or cold rolled and recovery annealed electrodeposited, optionally fluid melted tin plates. These substrates comprise recovery annealed substrates rather than recrystallized single reduced ETP or tinplate or double reduced tinplate. Differences in the microstructure of the substrate were not observed to substantially affect the Cr—CrOx coating.

  The material according to the invention can be used in combination with thermoplastic coatings, but also for applications where ECCS is traditionally used in combination with lacquers (ie heat-resistant pans such as tin pan molds or moderate It has been found that it can also be used as an alternative to conventional tin for applications with a moderate need for corrosion resistance (for products with a need for corrosion resistance).

  In one embodiment, the coated substrate is further provided with an organic coating consisting of either a thermosetting organic coating, or a thermoplastic single layer polymer coating, or a thermoplastic multilayer polymer coating. The Cr-CrOx layer provides excellent adhesion to organic coatings similar to that obtained by using conventional ECCS.

  In a preferred embodiment, the plastic polymer coating is a polymer coating system comprising one or more layers including the use of a thermoplastic resin such as polyester or polyolefin, but acrylic resin, polyamide, polyvinyl chloride, fluorocarbon resin Polycarbonates, styrene type resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalized polymers can also be included. For clarity:

  Polyester is a polymer composed of dicarboxylic acid and glycol. Examples of suitable dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and cyclohexanedicarboxylic acid. Examples of suitable glycols include ethylene glycol, propanediol, butanediol, hexanediol, cyclohexanediol, cyclohexanedimethanol, neopentyl glycol and the like. Three or more dicarboxylic acids or glycols can be used together.

  Examples of the polyolefin include a polymer or copolymer of ethylene, propylene, 1-butene, 1-pentene, 1-hexene or 1-octene.

  Examples of the acrylic resin include a polymer or copolymer of acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, or acrylamide.

  Examples of the polyamide resin include so-called nylon 6, nylon 66, nylon 46, nylon 610, and nylon 11.

  Polyvinyl chloride includes homopolymers and copolymers with, for example, ethylene or vinyl acetate.

  Examples of the fluorocarbon resin include tetrafluorinated polyethylene, trifluorinated monochlorinated polyethylene, hexafluorinated ethylene-propylene resin, polyvinyl fluoride, and polyvinylidene fluoride.

  For example, polymers functionalized with maleic anhydride grafts include, for example, modified polyethylene, modified polypropylene, modified ethylene acrylate copolymers, and modified ethylene vinyl acetate.

  Mixtures of two or more resins can also be used. Further, the resin can be mixed with an antioxidant substance, a heat stabilizer, a UV absorber, a plasticizer, a pigment, a nucleating agent, an antistatic agent, a release agent, an anti-tacking agent, and the like. The use of such thermoplastic polymer coating systems has been shown to provide superior performance, such as shelf life, in can making and can use.

  According to a second aspect, the present invention is embodied in a process for producing a coated steel substrate for packaging applications, the process comprising electrodeposition of a metal chromium-chromium oxide coating to the substrate, Electrodeposition of the metallic chromium-chromium oxide coating onto the substrate comprises a trivalent chromium compound, an optional chelating agent, an optional conductivity enhancing salt, an optional depolarizing agent, and an optional surfactant. Occurs in a single plating step from a plating solution that can contain and add acid or base to adjust pH.

  In one embodiment, the electrodeposition of the Cr-CrOx coating uses an electrolyte in which the chelator includes a formate anion, the conductivity enhancing salt includes an alkali metal cation, and the depolarizer includes a bromide-containing salt. Achieved.

  In one embodiment, the cationic species in the chelating agent, conductivity enhancing salt, and depolarizer is potassium. The advantage of using potassium is that the presence of the electrolyte in the electrolyte greatly increases the electrical conductivity of the solution over any other alkali metal cation, and thus the cell voltage required to drive the electrodeposition process. Is to deliver the greatest contribution to lowering.

  In one embodiment of the present invention, the composition of the electrolyte used to deposit the Cr—CrOx was 120 g / l basic chromium sulfate, 250 g / l potassium chloride, 15 g / l potassium bromide and 51 g / l. 0.2 g / l potassium formate. The pH was adjusted to a value between 2.3 and 2.8 measured at 25 ° C. by addition of sulfuric acid.

  According to the invention, the chromium-containing coating is preferably deposited from an electrolyte based on trivalent chromium at a bath temperature between 40 and 70 ° C., preferably at least 45 ° C. and / or at most 60 ° C.

  Surprisingly, it has been found that it is possible to electrodeposit a chromium-chromium oxide coating layer from this electrolyte in a single process step. According to the prior art, the addition of a buffer to an electrolyte such as boric acid is strictly required to allow electrodeposition of chromium metal to occur. In addition, it is this buffering effect that metal chromium and chromium oxide are deposited from the same electrolyte (buffering agents are necessary for electrodeposition of chromium metal, but eliminate the formation of chromium oxide and vice versa) Because of this, it is reported not possible. However, under conditions where a sufficiently large cathode current density is applied, it has been found that such addition of a buffering agent is not necessary for depositing chromium metal.

  The XPS depth profile was measured, and the measured peaks were Fe2p, Cr2p, Ols, Sn3d, and Cls. It was observed that the Cr layer consisted of a mixture of Cr oxide and Cr metal, and that the Cr oxide was mixed throughout the layer without being present as a separate layer on the outermost surface. This is also indicated by the O-peak that it is present throughout the Cr layer. In all cases, the Cr—CrOx layer has a shiny metallic appearance.

  In order for metal chromium electrodeposition to occur, a threshold value for the current density must be exceeded, which is a result of the evolution of hydrogen gas and the equilibrium of various (chelated) polychrome hydroxide complexes. It is thought to be closely related to the pH at the strip surface reaching a certain value. After exceeding this threshold value for current density, the electrodeposition of the chromium metal-chromium oxide coating layer is substantially linear with increasing current density according to Faraday's law, as observed with conventional electrodeposition of metals. Has been found to increase. The actual value of threshold current density appears to be closely related to the mass transfer conditions at the strip surface. That is, this threshold was observed to increase with increasing mass transfer rate. This phenomenon can be explained by the change in pH value at the strip surface. That is, at increased mass transfer rates, the supply of hydronium ions to the strip surface is increased and to maintain a specific pH level at the strip surface (which is clearly higher than the overall pH) under steady state process conditions. In addition, an increase in cathode current density is required. The validity of this hypothesis is supported by the results obtained from experiments where the overall electrolyte pH was varied between 2.5 and 2.8. That is, the threshold for current density decreases with increasing pH value.

  With respect to the electrodeposition process of Cr—CrOx coating from an electrolyte based on trivalent chromium, it is important to prevent / minimize the oxidation of trivalent chromium to its hexavalent state at the anode. The anode material must be selected. Formation of Cr (IV) can be prevented by using the hydrogen gas diffusion anode described below.

In one embodiment of the present invention, the formation of Cr (IV) uses one, two or more or only one hydrogen gas diffusion anode in which hydrogen gas (H ₂ (g)) is oxidized. Can be prevented. H ⁺ (proton) in the aqueous solution binds to one or more water molecules as, for example, hydronium ions (H ₃ O ⁺ ). When using an anode in which water (H ₂ O) is oxidized to oxygen (O ₂ (g)), undesired oxidation reactions such as formation of Cr (IV) occur at higher anode overvoltages Is prevented from oxidizing H ₂ (g) to H ⁺ (aq).

The reaction H ₂ (g) → 2H ⁺ (aq) + 2e ⁻ takes place at an anode voltage of 0.00V (SHE). The reaction 2H ₂ O → 4H ⁺ (aq) + O ₂ (g) + 4e ⁻ occurs at an anode voltage of 1.23 V (SHE). If an anode is used in which water is oxidized to oxygen, then reactions that were not possible when using an anode in which hydrogen gas is oxidized are possible.

One such undesirable oxidation reaction is the oxidation of Cr (III) to Cr (VI), which is a hydrogen gas diffusion anode (H ₂ (g) is oxidized to H ⁺ ). GDA) can be completely eliminated.

In one embodiment of the method of the present invention, H ₂ (g) is oxidized to H ⁺ (aq) at a current efficiency of at least 99%, preferably 100%, in a hydrogen gas diffusion anode. The higher the current efficiency, the smaller the likelihood of undesirable side reactions. Therefore, the current efficiency is preferably at least 99%, preferably 100%. Based on thermodynamic and kinetic considerations, the use of a hydrogen gas diffusion anode reduces the risk of Cr (III) oxidation when the anode operating voltage is too low for Cr (III) oxidation to occur. It can be argued that it will be completely excluded.

Thermodynamically, under standard conditions (ie a temperature of 25 ° C. and a pressure of 1 atm), an electrode voltage of> 0 V is already sufficient to oxidize H ₂ (g) to H ⁺ (aq). However, in order to oxidize H ₂ O to O ₂ (g), an electrode voltage of> 1.23 V is required. Cr (III) can only be oxidized to Cr (VI) if the electrode voltage is> 1.35V.

  The electrode voltage is measured against a standard hydrogen electrode. A standard hydrogen electrode (abbreviated as SHE) is a redox electrode that forms the basis of a thermodynamic measure of redox voltage. Its absolute electrode voltage is estimated to be 4.44 ± 0.02 V at 25 ° C., but forms the basis for comparison with all other electrode reactions, and the standard electrode voltage (E °) for hydrogen is Declared to be zero at all temperatures. The voltage of any other electrode is compared to the voltage of a standard hydrogen electrode at the same temperature.

  The equilibrium (zero current) voltage at that time can be calculated by filling the Nernst equation with the appropriate temperature, pressure and activity of the electrically active species. The anode actuation (non-zero current) voltage required to generate a specific anode current is the activation overvoltage (ie, the potential difference required to proceed with the electrode reaction) and the concentration overvoltage (ie, the concentration of the electrically active species at the electrode). Determined by the potential difference required to compensate for the gradient).

Based on the low anode overvoltage required for the oxidation of H ₂ (g) to H ⁺ (aq), the anode working voltage will always stay well below the value at which oxidation of Cr (III) can occur. (See FIG. 4 where the current is pointed to the anode voltage for SHE). First, this results in lower energy consumption in the electrodeposition process. Second, at anode voltages below about 1.35V, oxidation of Cr (III) to Cr (VI) is not possible (indicated by crossing arrows).

  In one embodiment, no depolarizer is added to the electrolyte. If a hydrogen gas diffusion anode is used, then no addition of a depolarizer to the electrolyte is necessary.

  The use of a hydrogen gas diffusion anode has the added advantage that the use of an electrolyte containing chloride is possible without the risk of chlorine formation. This chlorine gas can be harmful to the environment and workers and is therefore undesirable. This means that in the case of a Cr (III) electrolyte, the electrolyte can be partially or totally based on chloride. The advantage of using a chloride-based electrolyte is much higher when compared to electrolytes based solely on sulfate, thus lowering the cell voltage required to perform electrodeposition. As a result, energy consumption is reduced.

  The oxidation of dissolved hydrogen on the active electrocatalyst surface is a very fast process. Since the solubility of hydrogen in the liquid electrolyte is often low, this oxidation reaction can be easily controlled by mass transfer rate limiting. Porous electrodes are specifically designed to overcome mass transfer rate limiting. A hydrogen gas diffusion anode is porous comprising a three-phase interface of a solid electrocatalyst (eg platinum) applied to hydrogen gas, an electrolyte fluid and a conductive porous matrix (eg porous carbon or porous metal foam). It is the anode. The main advantage of using such a porous electrode is that it has a very large internal surface area for reactions contained in a small volume, a very reduced diffusion path from the gas-liquid interface to the reaction site. In combination with the length. This design greatly increases the mass transfer rate of hydrogen, while the true local current density decreases at a given total electrode current density, resulting in a lower electrode voltage.

  The gas diffusion anode assembly used in the electrodeposition method proposed in the present invention typically includes the use of the following functional elements (see FIG. 5). A gas diffusion anode consisting of a hydrophobic porous gas diffusion transport layer 3 combined with a gas supply chamber 1, a current collector 2 and a hydrophilic reaction layer 4 (see FIG. 5). The hydrophilic reaction layer is made of a network of micropores that are (partially) immersed in a liquid electrolyte. In some cases, the reaction layer comprises an outer proton exchange membrane 5 such as a Nafion® membrane, and diffusion of chemical species present in the liquid electrolyte other than the electrode surface inside the gas diffusion anode (anion or large) Such as neutral molecules) because these compounds may inhibit the action of the electrocatalytic sites and cause degradation of electrocatalytic activity.

  The main function of the gas supply chamber is to supply hydrogen gas evenly to the hydrophobic back side of the hydrogen gas diffusion anode. The gas supply chamber requires two connections: one for supplying hydrogen gas, and one releasing a small amount of hydrogen gas, present in trace amounts in the supplied hydrogen gas This is to prevent the accumulation of possible gas phase pollutants. The gas supply chamber often includes a channel-type structure to ensure that hydrogen gas is evenly distributed on the hydrophobic backside.

  A current collector 2 is (usually) attached to the hydrophobic back side 3 of the hydrogen gas diffusion anode to allow transport of current generated inside the anode to a rectifier (not shown in FIG. 5). This current collector plate must be designed to allow hydrogen gas to contact the back side of the hydrogen gas diffusion anode so that the hydrogen gas can be transported to the reaction side inside the gas diffusion anode. Typically this is accomplished by using a conductive plate with a large number of holes, a wire mesh or an expanded metal sheet made of, for example, titanium.

  The functions of the gas supply channel and current collector can also be combined into a single component, which is then pressed against the hydrophobic back side of the gas diffusion anode.

As hydrogen gas diffuses through the hydrophobic backside of the hydrogen gas diffusion anode, it contacts the hydrophilic portion of the anode, ie, the electrolyte present in the reaction layer (see FIG. 5, right side). At the gas-liquid interface (between 3 and 4), hydrogen gas dissolves in the electrolyte and is transported by diffusion to the electrocatalytic active site of the hydrogen gas diffusion anode. Usually, platinum is used as the electrocatalyst, but other materials such as platinum-ruthenium or platinum-molybdenum alloys can also be used. At the electrocatalytic site, the dissolved hydrogen is oxidized: the generated electrons are transported to the current collector 2 through the conductive matrix (usually a carbon matrix) of the gas diffusion anode, while hydronium ions (H ⁺ ) Diffuses through the proton exchange membrane into the electrolyte.

  In one embodiment, the coated substrate is on one or both sides from a thermosetting organic coating by a lacquering step, or a thermoplastic single layer, or a thermoplastic multilayer polymer by a film lamination step or a direct extrusion step. And further comprising an organic coating.

  In one embodiment, the plastic polymer coating is a polymer coating system comprising one or more layers including the use of thermoplastic resins such as polyester or polyolefin, but acrylic resin, polyamide, polyvinyl chloride, fluorocarbon resin, Polycarbonates, styrenic resins, ABS resins, chlorinated polyethers, ionomers, urethane resins and functionalized polymers; and / or copolymers thereof; and / or blends thereof may also be included.

Preferably, especially in the case of tinplate, the substrate is heated to a temperature between 35 ° C. and 65 ° C. in a sodium carbonate solution containing between 1 and 50 g / l Na ₂ CO ₃ prior to electrodeposition of Cr—CrOx. So that a cathode current density between 0.5 A / dm ² and 2 A / dm ² is applied for 0.5 to 5 seconds.

The sodium carbonate solution preferably contains at least 2 g / l and / or at most 5 g / l Na ₂ CO ₃ .

  The present invention will now be further described with reference to the following examples and figures, but the present invention is not limited thereto.

Example

Example 1
Not conventional passivation with a tin coating weight of 2.8gSn / m ² on both sides, the flow molten tin sheet (ordinary steel standards and carbonaceous amount), minimizing the tin oxide layer thickness In order to do so, an electrolysis pretreatment was performed. This was done by immersing the sheet in a sodium carbonate solution (3.1 g / l Na ₂ CO ₃ , temperature 50 ° C.) and applying a cathode current density of 0.8 A / dm ² for 2 seconds. . After rinsing with deionized water, the sample is kept at 50 ° C. consisting of 120 g / l basic chromium sulfate, 250 g / l potassium chloride, 15 g / l potassium bromide and 51.2 g / l potassium formate. It was immersed in the dripped trivalent chromium electrolyte. The pH of this solution was adjusted to 2.3 as measured at 25 ° C. by addition of sulfuric acid. Applying a cathode current density of 10 A / dm ² for about 1 second with a Cr—CrOx coating containing between 21-25 mg Cr / m ² (measured by XRF) using a platinized titanium anode as the counter electrode Was deposited on the surface. The sample so produced showed a shiny metallic appearance.

In order to investigate the passivating effect of the thin Cr—CrOx coating on the tinplate, the sample was subjected to a long-term storage test at a static humidity level of 40 ° C. and 80% RH. Next, the amount of tin oxide generated on the tinplate surface during storage was measured after exposure for 2 and 4 weeks, and the amount of tin oxide present on the sample before the storage test (referred to as “0 weeks”). Compare with The quantification of the tin oxide layer thickness is described in S.A. C. Britton, “Tin vs corrosion”, ITRI Publication No. 510 (1975), Chapter 4, using a colorimetric method. The tin oxide layer was reduced with a small controlled cathodic current in a 0.1% solution of hydrobromic acid (HBr) freed of oxygen by passing nitrogen. The progress of the reduction of the oxide is followed by voltage measurement and the charge passed for complete reduction (expressed in 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 shown in Table 1 including the performance of the same tinplate material passivated using hexavalent chromium, ie the reference material which is the so-called 311 passivated tin.

  The results show that the non-passivated tin treated according to the present invention to obtain a thin Cr—CrOx coating shows full stability in tin oxide growth and is sufficient in performance to the traditional 311 passivated tin It shows that it is comparable.

Example 2
A conventional, non-passivated, fluidly melted tin sheet (normal steel specification and carbon content) with a tin coating weight of 2.8 g Sn / m ² on both sides was first electropretreated. The tin oxide layer thickness was minimized. This was done by immersing the sheet in a sodium carbonate solution (3.1 g / l Na ₂ CO ₃ , temperature 50 ° C.) and applying a cathode current density of 0.8 A / dm ² for 2 seconds. After rinsing with deionized water, the sample is kept at 50 ° C. consisting of 120 g / l basic chromium sulfate, 250 g / l potassium chloride, 15 g / l potassium bromide and 51.2 g / l potassium formate. It was immersed in the dripped trivalent chromium electrolyte. The pH of this solution was adjusted to 2.3 as measured at 25 ° C. by adding sulfuric acid. Cr—CrOx coating containing between 65-75 mg Cr / m ² (measured by XRF) by applying a cathode current density of 15 A / dm ² for about 1 second using a platinized titanium anode as the counter electrode Was deposited on the surface. All samples so produced showed a shiny metallic appearance. Typical SEM images are shown in FIGS. 1 and 2, which show the deposition of very fine particles of chromium metal-chromium oxide on the tin surface.

  The sheet was then lacquered by applying a commercially available epoxy anhydride lacquer system (Vitalure ™ 120 supplied by Akzo Nobel). Subsequently, the lacquered sheet was locally deformed by Erichsen cupping.

  In order to analyze the performance of the chromium-chromium oxide coated tin, several sterilization tests were performed to evaluate the wet adhesion performance on flat and deformed materials. As shown in Table 2, a total of 5 different sterile media were used during these tests.

  After sterilization, the level of lacquer adhesion of the panels was evaluated for blister formation (blowing size and number) and visual discoloration (cross cut and tape test (according to ISO 2409: 1992)). The performance of the same tinplate material passivated using hexavalent chromium, ie the so-called 311 passivated tin, is shown in Table 3. The performance ranking is 0 to 5 on a scale of 0 Is an excellent performance and 5 is a very poor performance, the results were averaged over the number of observations and scored in decimal values.

  The inventors have found that tinplate variants made in accordance with the present invention consistently perform as well or better compared to standard tinplates passivated using hexavalent chromium (ie, reference). I found out that I did it. What is amazing is the fact that no sulfur discoloration is found for the material according to the present invention, which is difficult to achieve with conventional passivated tinplates and an alternative immobilization without hexavalent chromium for tinplates. It is well-known that it is difficult to achieve by computerization.

Example 3
The tinplate coil (normal steel specification and carbon content) without any metal coating was processed in a processing line running at a line speed of 20 m / min. The processing sequence consists of alkaline cleaning of the steel by running the strip through a solution containing 30 ml / 1 commercial cleaner (Percy P3) and 40 g / l NaOH kept at 60 ° C. for about 10 seconds. Started. During strip cleaning, an anode current density of 1.3 A / dm ² was applied. After rinsing with deionized water, the steel strip was passed through an acid solution for about 10 seconds to activate the surface. The acid solution consisted of 50 g / l H ₂ SO ₄ and was kept at 25 ° C. After rinsing with deionized water, the strip was passed through an electroplating bath containing an electrolyte composed mainly of trivalent chromium kept at 50 ° C. The electrolyte consisted of 120 g / l basic chromium sulfate, 250 g / l potassium chloride, 15 g / l potassium bromide and 51.2 g / l potassium formate. The pH of this solution was adjusted to 2.3 as measured at 25 ° C. by adding sulfuric acid. The electroplating bath contained a set of anodes made of platinized titanium. During strip processing, a cathode current density of about 17 A / dm ² was applied over just 1 second and a 60-70 mg Cr / m ² chromium-chromium oxide coating (measured by XRF) was electrodeposited onto the tinplate surface. . All samples so produced showed a shiny metallic appearance. Typical SEM images are shown in FIGS. 1 and 2, which show very fine particle deposition of chromium metal-chromium oxide on the steel surface.

  The material so produced was applied by heat sealing to a commercially available PET film having a thickness of 20 micrometers through a coating line. After film lamination, the coated strip was post-heated to a temperature above the melting point of PET by conventional processing methods for metal PET lamination, followed by quenching with room temperature water. The same procedure was followed for the fabrication of the reference material using ECCS commercially manufactured coils.

  The laminated material was used to make a standard food DRD can (211 × 400). In all cases, the dry adhesion of the PET film to the can wall was good. This was confirmed by measuring the T peel force of the PET film attached to the can wall. The peel force showed similar values for the PET film applied to both the material according to the invention and the commercial ECCS (about 7 N / 15 mm).

  Subsequently, the DRD cans were filled with different media, closed, and subjected to sterilization. In order to simulate and observe the effects of accidental coating damage, several cans with scratches on the can walls were treated. A summary of the types of sterilization tests performed is shown in Table 4.

  After sterilization, the DRD cans were cooled to room temperature, rinsed, rinsed and dried for 1 day. The presence of corrosion spots and blisters on the bottom and can walls were visually judged. The results show that the sterilization performance of the material according to the present invention is generally slightly inferior compared to the ECCS reference, as shown in Table 5. The material appears to be particularly susceptible to corrosion / coating delamination after coating damage. However, since these sterilization tests are very harsh, in practice the material according to the invention can be used in applications involving particularly selected sterilizations.

  The performance ranking is a scale from 0 to 5, with 0 being excellent performance and 5 being very poor performance.

Example 4
A tin plate coil (normal steel specification and carbon content) without any metal coating was processed on the same processing line as described in the previous examples to apply a Cr-CrOx coating.

  The sheet cut from this coil was then lacquered by applying a commercially available epoxy phenol lacquer system (Vitalure TM345 supplied by AkzoNobel). Subsequently, the lacquered sheet was locally deformed by Erichsen cupping.

  In order to analyze the performance of the tinplate coated with chromium-chromium oxide, several sterilization tests were performed to evaluate the wet adhesion performance on flat and deformed materials. A total of 5 different sterile media were used during these tests, as shown in Table 6.

  After sterilization, the panels were evaluated for lacquer adhesion (by cross-cut and tape test (ISO 2409: 1992 (E))), blister formation (blowing size and number) and level of visual discoloration. The overall results are shown in Table 7, including the performance of the reference material using commercial ECCS. The rank of performance is a scale from 0 to 5, with 0 being excellent performance and 5 being very poor performance.

  The present inventors have found that Cr—CrOx coated tin plate material produced according to the present invention consistently exhibits the same performance as conventional ECCS.

1 and 2 show typical SEM images showing the deposition of very fine particles of metal chromium-chromium oxide on the surface. FIG. 1 relates to a tin plate base material, and FIG. 2 relates to a tin plate base plate base material. 1 and 2 show typical SEM images showing the deposition of very fine particles of metal chromium-chromium oxide on the surface. FIG. 1 relates to a tin plate base material, and FIG. 2 relates to a tin plate base plate base material. FIG. 3 shows an overview of various packaging applications. The grade of packaging steel on the X-axis and the typical thickness range on the Y-axis are shown for those applications in which the packaging steel substrate according to the invention can be used. FIG. 4 shows the dotted current with respect to the anode voltage (SHE). FIG. 5 shows a schematic diagram of a gas diffusion anode.

DESCRIPTION OF SYMBOLS 1 Gas supply chamber 2 Current collector 3 Porous gas diffusion transport layer 4 Hydrophilic reaction layer 5 Proton exchange membrane

Example 3 (not part of the present invention)
The tinplate coil (normal steel specification and carbon content) without any metal coating was processed in a processing line running at a line speed of 20 m / min. The processing sequence consists of alkaline cleaning of the steel by running the strip through a solution containing 30 ml / 1 commercial cleaner (Percy P3) and 40 g / l NaOH kept at 60 ° C. for about 10 seconds. Started. During strip cleaning, an anode current density of 1.3 A / dm ² was applied. After rinsing with deionized water, the steel strip was passed through an acid solution for about 10 seconds to activate the surface. The acid solution consisted of 50 g / l H ₂ SO ₄ and was kept at 25 ° C. After rinsing with deionized water, the strip was passed through an electroplating bath containing an electrolyte composed mainly of trivalent chromium kept at 50 ° C. The electrolyte consisted of 120 g / l basic chromium sulfate, 250 g / l potassium chloride, 15 g / l potassium bromide and 51.2 g / l potassium formate. The pH of this solution was adjusted to 2.3 as measured at 25 ° C. by adding sulfuric acid. The electroplating bath contained a set of anodes made of platinized titanium. During strip processing, a cathode current density of about 17 A / dm ² was applied over just 1 second and a 60-70 mg Cr / m ² chromium-chromium oxide coating (measured by XRF) was electrodeposited onto the tinplate surface. . All samples so produced showed a shiny metallic appearance. Typical SEM images are shown in FIGS. 1 and 2, which show the deposition of very fine particles of metallic chromium-chromium oxide on the steel surface.
It relates to a DRD can with scratches.

Example 4 (not part of the present invention)
A tin plate coil (normal steel specification and carbon content) without any metal coating was processed on the same processing line as described in the previous examples to apply a Cr-CrOx coating.

Claims (12)

A coated steel substrate for packaging applications,
1. 1. Conventional non-passivated electrodeposited, optionally fluid melted tin, or Including cold rolled, recovery annealed and electrodeposited, optionally fluid melted tinplate,
A steel substrate for packaging, wherein one or both sides of the substrate is coated with a metallic chromium-chromium oxide coating layer produced in a single process step using a trivalent chromium electroplating process. The metal chromium-chromium oxide layer is preferably between 20 mg / m ² and 140 mg / m ² , more preferably between 40 mg / m ² and 90 mg / m ² , and most preferably 60 mg / m ² and 80 mg / m ^2. A coated substrate for packaging applications according to claim 1 having a total chromium content of between ² .   The coated substrate further comprises an organic coating consisting of either a thermosetting organic coating, a thermoplastic single layer coating, or a thermoplastic multilayer polymer coating, preferably the thermoplastic polymer coating is , Thermoplastic resins such as polyester or polyolefin, acrylic resin, polyamide, polyvinyl chloride, fluorocarbon resin, polycarbonate, styrene type resin, ABS resin, chlorinated polyether, ionomer, urethane resin and functionalized polymer; and / A coated substrate for packaging applications according to claim 1 or 2, wherein the coated substrate comprises one or more polymer coating systems comprising: or a copolymer thereof; and / or a blend thereof. 1. 1. Conventional non-passivated electrodeposited, optionally fluid melted tin, or For packaging applications by depositing a metal chromium-chromium oxide coating on a substrate for packaging applications, including cold rolled, recovery annealed, electrodeposited and optionally fluid melted tinplate. A method for producing a coated steel substrate, comprising:
Plating containing a mixture of trivalent chromium compound, chelating agent, optional conductivity enhancing salt, optional depolarizer, optional surfactant, optionally with acid or base added to adjust pH Electrically depositing the metal chromium-chromium oxide coating on the substrate from a solution in a single process step.   The method of claim 4, wherein the chelating agent comprises a formate anion, the conductivity enhancing salt comprises an alkali metal cation, and the depolarizing agent comprises a bromide containing salt.   The method according to claim 4 or 5, wherein the cationic species in the chelating agent, the conductivity enhancing salt and the depolarizing agent is potassium.   The coated substrate comprises on one or both sides a thermosetting organic coating by a lacquering step, or an organic coating consisting of a thermoplastic single layer or a thermoplastic multilayer polymer by a film laminating step or a direct extrusion step Preferably, the plastic polymer coating is polyester or polyolefin, acrylic resin, polyamide, polyvinyl chloride, fluorocarbon resin, polycarbonate, styrene type resin, ABS resin, chlorinated polyether, ionomer, urethane resin And / or thermoplastic resins such as functionalized polymers; and / or copolymers thereof; and / or polymer coating systems comprising one or more layers comprising a blend thereof. Description Method.   8. An anode according to any of claims 4 to 7, wherein the anode is selected to reduce or eliminate oxidation of Cr (III) ions to Cr (VI) ions during the plating step, such as a gas diffusion anode. The method according to claim 1.   The chromium-containing coating is preferably deposited from an electrolyte based on trivalent chromium at a temperature between 40 ° C. and 70 ° C., preferably at least 45 ° C. and / or at most 60 ° C. 9. The method according to any one of items 1 to 8.   A tin-coated substrate for packaging applications is subjected to an electrolytic pretreatment to minimize the thickness of the tin oxide layer before it is coated on one or both sides with a metal chromium-chromium oxide coating layer. 10. A method according to any one of claims 4 to 9.   11. The method of claim 10, wherein the electrolytic pretreatment comprises the steps of immersing a tin coated substrate in a sodium carbonate solution and applying a cathode current density. The sodium carbonate solution consists of between 2 and 5 g / l Na ₂ CO _{3 at} a temperature between 35 ° C. and 65 ° C., and has a cathode current density between 0.5 A / dm ² and 2 A / dm ^2. 12. A method according to claim 11, wherein the method is applied for 0.5 to 5 seconds.