Method for electrodepositing a functional or decorative chromium layer from a trivalent chromium electrolyte.

Abstract

The present invention relates to a method for electrodepositing a functional or decorative chromium layer on a metal substrate in an electrodeposition process from an aqueous electrolyte solution that is halide ion-free and boric acid-free, and to the coated products obtained thereby.

Description

[Technical Field]

[0001] The present invention relates to a method for electrodepositing a functional or decorative chromium layer onto a metal substrate using a trivalent chromium electrolyte. [Background technology]

[0002] Hexavalent chromium electrodeposition has been used for many years to form decorative and durable coatings with excellent wear resistance and corrosion resistance. However, hexavalent chromium baths are now subject to increasingly stringent scrutiny due to the toxicity of the baths and their impact on the environment and worker health.

[0003] Therefore, for health and safety reasons, chrome plating must be applied using a Cr(III) electrolyte. Many commercially available Cr(III) electrolytes for applying decorative chrome plating are available on the market. Typical applications include automotive parts (interior and exterior), sanitary and plumbing fixtures, furniture, and hand tools.

[0004] For certain applications, such as the manufacture of photovoltaic devices on mild steel substrates, a diffusion barrier layer is required. Such a barrier layer prevents iron or other harmful elements from diffusing from the steel substrate into the solar cell, which is deposited at temperatures up to 600°C. One example of a barrier layer combination is a chromium layer on a nickel-plated steel substrate. The term "harmful" refers to elements that negatively affect the efficiency of the solar cell.

[0005] The distinction between functional chromium layers and decorative chromium layers is generally understood as follows:

[0006] [Table 1]

[0007] Decorative chrome coating is typically applied over a double nickel undercoat. The nickel layer provides corrosion resistance and smooths the substrate surface. The principle is that by applying two nickel layers (the first being semi-glossy with a columnar structure (13-30 μm) and the second being glossy with a layered structure (5-20 μm)), the glossy nickel provides cathodic protection against the semi-glossy nickel, resulting in excellent corrosion resistance. The glossy nickel acts as the anode, sacrificingly protecting the semi-glossy nickel. As a result, corrosion spreads laterally rather than penetrating the substrate. Decorative chrome coating has numerous micro-cracks and micro-pores. Because these micro-defects are spread uniformly across the chrome surface, corrosion is not localized and therefore progresses slowly.

[0008] Unfortunately, commercially available Cr(III) electrolytes commonly used for depositing functional or decorative chromium coatings have the following drawbacks: i) The complex chemical properties of electrolytes (many components), especially the buffering agents, which are difficult to control, maintain, and replenish. ii) Cr(III) electrolytes typically contain boric acid as a buffer. Since boric acid is toxic and potentially dangerous, it is desirable to avoid its presence in the electrolyte. iii) Chloride-based electrolytes: Risk of chlorine generation at the anode, depolarizer required to suppress Cr(VI) formation at the anode (bromides are often used for this purpose), moderate chromium deposition rate (0.2 μm min) -1 ). iv) Sulfuric acid-based electrolyte: Slow chromium deposition rate (0.05 μm min) -1 ). v) Commercially available trivalent chromium baths often result in cracked coatings after heat treatment. [Overview of the project] [Problems that the invention aims to solve]

[0009] The objective of the present invention is to electrodeposit a decorative or functional chromium layer onto a metal substrate using an electrolyte solution containing a trivalent chromium compound.

[0010] Another object of the present invention is to electrodeposit a decorative or functional chromium layer on a metal substrate from an electrolyte solution containing a trivalent chromium compound and a minimal amount of other compounds for use in photovoltaic applications.

[0011] Another object of the present invention is to provide a method for electrodepositing a decorative or functional chromium layer on a metal substrate that complies with REACH.

[0012] Another object of the present invention is to provide a method for electrodepositing a decorative or functional chromium layer on a metal substrate that has a higher deposition rate than known methods.

Means for Solving the Problems

[0013] One or more of the above objects are achieved by a method for electrodepositing a functional or decorative chromium layer on a metal substrate in a batch or continuous electrodeposition process from an aqueous electrolyte solution free of halide ions and free of boric acid, wherein the aqueous electrolyte solution comprises i) a trivalent chromium compound formed by a water-soluble chromium (III) salt, wherein the aqueous electrolyte solution contains 50 mM to 1000 mM of Cr 3+ ions; ii) sodium sulfate or potassium sulfate in a total amount of 25 to 2800 mM; iii)

Number

Brief Description of the Drawings

[0014] [Figure 1] Figure 1 is a diagram showing a single-pulse electrodeposition process with a pulse width of 1 second as a function of current density. [Figure 2] Figure 2 is a diagram showing the relationship between the number of pulses and the amount of deposited chromium adhesion when the current density is 26 A / dm2, the pulse width is 1 second, and the interpulse period is 10 seconds. [Figure 3] Figure 3 is a diagram showing the decrease in process efficiency with an increasing interpulse period. [Figure 4] Figure 4 is a diagram showing SEM images of the chromium surface obtained by a single-pulse process and a multi-pulse process.

Modes for Carrying Out the Invention

[0015] The practical minimum off time is 0.1 seconds. In a shorter time, relaxation of the necessary concentration gradient including the pH of the diffusion boundary layer near the cathode and establishment of a new chemical equilibrium of the Cr(III) complex cannot be obtained during the period when the current is off.

[0016] The use of trivalent chromium compounds avoids the use of hexavalent chromium in the electrolyte, thus making this method REACH compliant. Since the electrolyte does not contain halide ions, the formation of toxic gases such as chlorine and bromine at the anode can be prevented. Furthermore, buffering agents such as boric acid (H3BO3), commonly used to prevent hexavalent chromium formation at the anode during electrodeposition, are not present in the electrolyte. Even without boric acid, chromium metal deposits under the conditions of the method according to this invention. The electrolyte does not contain depolarizing agents such as potassium bromide. The absence of this compound prevents the risk of bromine formation at the anode.

[0017] The electrodeposition process may be a batch electrodeposition process or a continuous electrodeposition process.

[0018] The preferred metal substrate is a non-alloy or low-alloy steel substrate. The steel substrate may be of various thicknesses, preferably 25 μm to 3 mm. Thinner thicknesses form flexible solar cell modules, while thicknesses exceeding 0.3 mm allow for rigid shapes or direct integration into building elements, in which case an electrical insulation layer is applied. The non-alloy or low-alloy steel includes non-alloy or low-alloy mild steel, and low-carbon (LC), very low-carbon (ELC), or ultra-low-carbon (ULC) steels may be used, for example, steels DC01 to DC07 as defined in EN 10130:2006 in Table 2 may be used. Preferably, the surface condition of the steel is glossy (Ra ≤ 0.4 μm, EN 10130:2006) or mirror-finish (Ra ≤ 0.10 μm, more preferably Ra ≤ 0.08 μm) to minimize the adverse effects that may occur due to surface roughness. Non-alloy or low-alloy steels include cold-rolled sections, or low-alloy high-tensile (HSLA) steel may also be selected. These steels may be used when higher tensile strength of the steel substrate is required. To avoid misunderstanding: The types of steel in non-alloy or low-alloy steel substrates mentioned above explicitly exclude stainless steel. Stainless steel is an alloy steel containing at least 10.5 wt.% Cr. Chromium is expensive. The method according to the present invention makes it possible to use a steel substrate that is less expensive than stainless steel, while still providing the corrosion resistance and protection against poisoning required for photovoltaic devices mounted on the steel. Furthermore, metal substrates equipped with a functional or decorative chromium layer according to the present invention may also be used for other applications where the functional and / or decorative properties of the chromium layer are required.

[0019] In the context of the present invention, pulsed electrodeposition comprises or consists of multiple current pulses (i.e., two or more) of a selected current density and pulse width, followed by an interpulse period in which the current density is set to 0. It should be noted that a current density of 0 during the interpulse period encompasses very low current densities at the cathode or anode, which have no significant effect on the electrodeposition during the interpulse period and have the same technical effect as a current density of exactly 0. This is because the interrupted electrodeposition process, during periods when the current is off, leads to the relaxation of the concentration gradient, including the pH of the diffusion boundary layer near the cathode, and the establishment of a new chemical equilibrium for the Cr(III) complex, which occurs even at a current density of 0, but the same effect occurs at a very low current density during the interpulse period. However, there appears to be no technical advantage in intentionally selecting such a very low current density, and therefore a preferred embodiment is to select a current density of 0 during the interpulse period. In one embodiment, the pulse width is at least 0.1 seconds, and the interpulse period is at least 0.1 seconds.

[0020] The terms “comprises” and their variations are not restrictive when they appear in this specification and the claims. When used in reference to a composition, “comprises” means that at least the components described are present in the described amounts or ranges. The terms “consists of” and their variations are restrictive when they appear in this specification and the claims. When used in reference to a composition, “consists of” means that the components described are present in the described amounts or ranges, and that other components may be present in the described amounts or ranges, unless indicated as optional elements (which may be present in a given amount, or not present at all, or not present in an amount that substantially affects the function of the invention). This also means that the addition of unavoidable impurities or ineffective components is considered not to substantially affect the function of the invention. This is to prevent the addition of components that do not substantially affect the function of the invention, which may be added solely for the purpose of easily circumventing the claims by adding substantially inert components. The terms "consisting only of" and their variations, when appearing in this specification and the claims, have a limiting meaning, meaning that only the components described are present in the described amounts or ranges, and that no other components are present except for unavoidable impurities.

[0021] The term "halide ion-free and boric acid-free" electrolyte means that the aqueous electrolyte solution does not contain amounts of halide ions and boric acid that substantially affect the action of the present invention. The buffering effect of boric acid claimed in prior art electrolytes is not required, nor even desired, in the electrolyte and method according to the present invention.

[0022] In embodiments of the present invention, the electrolyte aqueous solution consists of the following, and preferably consists only of the following. i) A trivalent chromium compound formed by a water-soluble chromium(III) salt, where the electrolyte aqueous solution is 50 mM to 1000 mM Cr3+ Contains ions; ii) Sodium sulfate or potassium sulfate in a total concentration of 25 to 2800 mM; iii)

number

[0023] In one embodiment, in a batch electrodeposition process, the pulse width is 0.1 to 2.5 seconds, preferably 0.5 to 2.5 seconds, and the interpulse period is 0.1 to 5 seconds, preferably 0.5 to 5 seconds.

[0024] In one embodiment, in a continuous electrodeposition process, the pulse width is 0.1 to 2.5 seconds, preferably 0.5 to 2.5 seconds, and the interpulse period is 0.1 to 5 seconds, preferably 0.5 to 5 seconds.

[0025] In a preferred embodiment, in a continuous electrodeposition process, the pulse width is 0.1 to 2 seconds, preferably 0.5 to 2 seconds, and the interpulse period is 0.1 to 2 seconds, preferably 0.5 to 2 seconds.

[0026] In a preferred embodiment, the aqueous electrolyte solution (also referred to herein as the “electrolyte”) consists of compounds within the range described herein above, and more preferably consists only of compounds within the range described herein above.

[0027] Preferably, the temperature of the electrolyte during electrodeposition is a maximum of 55°C, and more preferably a maximum of 50°C. The preferred minimum temperature of the electrolyte during electrodeposition is 35°C.

[0028] Preferably, the pH of the electrolyte is 2.00 to 3.00. All references to pH refer to pH values ​​measured at 25°C. More preferably, the pH is 2.25 to 2.75.

[0029] It should be noted that optional sulfuric acid, sodium hydroxide, or potassium hydroxide should only be added if the pH needs to be adjusted to a desired value. If the pH is already at the desired value, such addition is not necessary.

[0030] The complexing agent is a formate salt, preferably sodium formate or potassium formate.

[0031] Preferably, a complexing agent and Cr 3+ The molar ratio is 2.0:1.

[0032] Optional surfactants may be added as needed to facilitate the release of hydrogen gas bubbles formed during electrodeposition from the substrate. By non-limiting example, the inventors used 2–4 mL / L of TriChrome Regulator LR as recommended in the technical data sheet provided by the supplier. Other surfactants may also be used, and those skilled in the art will have no problem selecting a suitable surfactant and the amount to be added according to the relevant technical data sheet. The inventors noted that surfactants are generally not necessary in continuous processes, particularly when the substrate is a strip and the continuous process is carried out in a strip electrodeposition line, as the inherent relative motion between the electrolyte and the substrate already removes any bubbles from the substrate.

[0033] When used in photovoltaic applications, the thickness of the chromium coating should be 10–1000 nm. If the chromium coating is free of defects, the chromium coating itself can function as a barrier layer. However, in many cases, a nickel layer is preferably used between the substrate and the chromium layer, and the chromium and nickel layers together form a barrier layer. The nickel layer smooths the steel substrate and provides some insurance in case the chromium layer contains any defects or pinholes despite careful handling. The underlayer is not particularly limited as long as it can form a smooth, defect-free layer between the steel substrate and the chromium layer on top. A copper layer of 50–300 nm has also been shown to be useful and effective as an underlayer. Preferably, the Cu layer is 50–150 nm (e.g., about 100 nm) followed by a Cr layer of 450–550 nm (e.g., about 500 nm).

[0034] In the barrier layer according to the present invention, the thickness of the nickel layer is 0.25 to 5.5 μm, and the thickness of the chromium layer is 0.01 μm (10 nm) to 1.0 μm (1000 nm). In the presence of a dielectric layer, the Ni and Cr layers may be thinner than when there is no dielectric layer. The minimum preferred thickness of the chromium layer is 15 nm. The maximum preferred thickness of the chromium layer is up to 800 nm, preferably up to 700 nm. The minimum preferred thickness of the nickel layer is 0.4 μm. The maximum preferred thickness of the nickel layer is up to 3.5 μm, preferably up to 2.5 μm.

[0035] In a preferred embodiment, the thickness of the nickel layer is 1.75 to 2.5 μm, and / or the thickness of the chromium layer is 0.450 to 0.550 μm. These layer thicknesses are particularly suitable for the manufacture of PV modules that require high process temperatures (for example, in CIGS solar cell technology). In monolithic module manufacturing methods, a dielectric layer is required, so the nickel and chromium layers may be thin, and the dielectric layer can also prevent the migration of harmful elements such as iron and manganese to the CIGS layer, depending on the properties of the coating.

[0036] The chromium coating needs to be defect-free and crack-free to prevent the steel substrate from interfering with the functionality of the PV application. With commercially available trivalent chromium baths, cracked coatings were obtained, depending on the thickness, either before or after annealing.

[0037] If a cold-rolled steel substrate needs to be recrystallized or recovery annealed, the annealing must be performed before applying an optional nickel layer or an optional copper and chromium layer, because otherwise, harmful components may diffuse into the nickel, copper, or chromium layer during the recrystallized or recovery annealing, diffuse through the molybdenum back contact layer during the growth of the CIGS absorption layer, and eventually reach the CIGS absorption layer. The inventors have found it important to keep the iron content in the CIGS absorption layer as low as possible, preferably less than 20 ppm, and more preferably less than 7 ppm.

[0038] Since elements (such as Fe and Mn) negatively affect the efficiency of PV applications, the diffusion of these harmful elements from the substrate should ideally be reduced to less than 10 ppm, provided that the nickel, copper, and chromium layers are free of defects.

[0039] The chromium coating deposited according to the present invention provides good protection against elemental diffusion from the steel substrate up to a maximum temperature of 650°C.

[0040] The method according to the present invention is suitable for use in batch processes, such as rack electrodeposition or piecewise electrodeposition, and in continuous processes, such as continuous processes for strip material electrodeposition.

[0041] In embodiments of the present invention, the line speed of the electrodeposition line in the continuous electrodeposition process is at least 50 m / min, preferably at least 100 m / min. [Examples]

[0042] Two variations of HILAN® nickel-plated steel coil were used as the base material: a variation with high surface roughness and a dull surface appearance (Ra minimum 0.6, maximum 2.5 μm), and a polished finish variation with low surface roughness and a glossy appearance (Ra 0.2 μm or less). HILAN®, manufactured by Tata Steel, is a cold-rolled steel strip product electroplated with bright nickel. Bright nickel creates an ultra-hard, ultra-glossy surface, making it suitable for forging and deep drawing. Bright nickel is produced by electrodepositing a 0.5-3.0 μm bright nickel layer onto a cold-rolled steel strip, resulting in low contact resistance and high corrosion resistance.

[0043] This material was activated by immersion in a 50 g / L sulfuric acid solution at room temperature for 10 seconds. After activation, it was subjected to a 10 A / dm² test using a nickel anode in an electrolyte solution at 30°C. 2 A Woods nickel strike layer was applied at the specified cathode current density. The electrolyte aqueous solution contained 240 g / L nickel(II) chloride hexahydrate and 125 mL / L 37% hydrochloric acid.

[0044] The electrolyte aqueous solution for electrodeposition of chromium coating is prepared as follows:

[0045] [Table 2]

[0046] The electrolyte was treated to remove sulfites, as disclosed in EP3428321-A1, and the electrolyte temperature was 43°C.

[0047] The chromium deposition amount was measured using inductively coupled plasma-mass spectrometry (ICP-MS), a benchtop spectrometer (SPECTRO XEPOS), or a Byk handheld XRF-spectrometer (Model 4443). The inventors observed that the value obtained by ICP-MS was directly proportional to the total electrodeposition time, and the current efficiency corresponded to the current efficiency from previous experiments and that reported in the literature. When measured with an XRF-spectrometer, the chromium deposition amount tended to be underestimated, but with a simple calibration, the benchtop and handheld values could be compared with the values measured by ICP-MS.

[0048] The inventors found that when the nickel-plated substrate was electroplated in this solution for an electrodeposition time of 1 second, the chromium layer had a shiny appearance at low current densities, but shifted to a considerably dull appearance at high current densities or long electrodeposition times. This means that when electroplating by this method, the thickness of the shiny layer is limited (see Figure 1). This change from a shiny to a dull appearance can be easily confirmed by the naked eye and is confirmed by gloss measurement. The maximum chromium deposition amount with the resulting shiny appearance was about 150 mg / m 2 .

[0049] The inventors also found that when the current was interrupted, a shiny coating could be obtained even with a longer total electrodeposition time. During the interruption, hydrogen that also occurs during electrodeposition forms bubbles on the surface, and these bubbles are stimulated to separate from the electroplated metal substrate, for example, by agitation, shaking, or mechanical action. Then, the next electrodeposition process can be carried out on a surface without hydrogen bubbles each time. The inventors believe that the removal of these hydrogen bubbles is very important in the production of shiny chromium-plated surfaces. By intermittent removal of hydrogen and intermittent electrodeposition, a very shiny surface and a much thicker chromium layer can be obtained (Figure 2). When applied by this method, there seems to be no limit to the thickness of the chromium layer, and a layer up to 2 μm could be applied.

[0050] In decorative chromium electrodeposition, color is one of the most important coating characteristics. Since different parts plated with Cr(III) and Cr(VI) electrolytes can be combined without noticing the color difference, it is desirable that the color from Cr(III) electrolyte be similar to that from Cr(VI) electrolyte.

[0051] Table 2 shows the results of several color and gloss measurements to obtain an impression. Some of these measurements are plotted in Figure 1 (indicated by *). Objective evaluation of the gloss of a smooth surface can be obtained using a reflectometer operating according to ISO 2813:2014, such as the Byk micro-TRI-gloss from BYK-Gardner GmbH, and the measurement angle (20, 60, or 85°) may be selected depending on the level of reflectance. Gloss is defined as an optical property of a surface and is characterized by its ability to specularly reflect light (ISO 4618:2014). ISO 2813 defines three measurement angles, specifying that 20° should be used for high-gloss samples and 60° for medium-gloss samples. The reflectometer obtains gloss unit values ​​as shown in Table 2.

[0052] [Table 3]

[0053] This table shows current density (i), pulse time (t), and interpulse period (t). off The pulse count (#) is shown. The amount of deposited Cr, as well as parameters L, a, and b, are parameters in the CIELAB color space. The gloss unit (GU) is the result from the reflectometer, and the angle is the angle used for the measurement. The "glossy" column is the human interpretation of the deposited layer, either "glossy" or "dull." The last column indicates which measurements are presented in Figure 1.

[0054] These results indicate that a thicker, more lustrous chromium layer can be deposited by an interrupted electrodeposition process using the trivalent chromium electrolyte according to the present invention, and that a layer of 4000 mg / m² can be deposited. 2 This demonstrates that layers exceeding a certain threshold can be easily obtained. The preferred "on-time" is 0.1 to 2 seconds.

[0055] The inventors' explanation for this remarkable improvement is that, during periods when the current is off, the intermittent electrodeposition process leads to a relaxation of the concentration gradient, including the pH of the diffusion boundary layer near the cathode, and the establishment of a new chemical equilibrium for the Cr(III) complex. Furthermore, the interruption allows for the dissipation, removal, or active removal of hydrogen generated during electrodeposition from the cathode surface. As a result, chromium oxide formation during electrodeposition can be prevented. Evidence is shown by the results of XPS performed on two samples (corresponding SEM images are shown in Figure 4). Clearly, the dull sample contains a large amount of chromium oxide, while the shiny sample does not. The electrolyte composition, temperature, pH, and current density are identical for both examples in Table 3.

[0056] [Table 4]

[0057] Known trivalent chromium electrolytes for electrodeposited decorative chromium layers contain boric acid as a buffer. This ensures that the pH of the diffusion boundary layer is maintained at the set value. The prior art explicitly states that without these buffers, mainly chromium oxide, or chromium oxide alone, will be deposited; therefore, in this known art, the inclusion of boric acid is a prerequisite for depositing metallic chromium.

[0058] The process according to the present invention makes it possible to deposit a decorative chromium layer without using this boric acid buffer, thereby simplifying the electrolyte.

[0059] The inventors have also found that the total process time of the intermittent electrodeposition process can be limited by adding a surfactant to the electrolyte. This surfactant promotes the removal of hydrogen generated during electrodeposition. In most cases, the interpulse period may be shortened to less than 2 seconds. If the interpulse period is too short, hydrogen cannot be removed sufficiently effectively, and the establishment of a new chemical equilibrium for the Cr(III) complex during the period of zero current density cannot be obtained. This results in a dull surface of the chromium layer. A preferred interpulse period ("off-time") is 0.1 to 2 seconds.

[0060] If the interval between pulses becomes too long, complete equilibrium is reached again. The pH of the diffusion boundary layer near the cathode drops to the average value of the electrolyte. This means that in the next pulse, the pH of the cathode must first be raised (to obtain a lower pH value) before electrodeposition begins. As a result, the process efficiency decreases, which is shown in Figure 3. This figure shows 8 and 20 pulses at 26 A / dm². 2 This shows the amount of chromium deposited by a 1-second current pulse. Clearly, the amount of chromium deposited decreases significantly when the off-time is extended from 2 seconds to 5 seconds. When the off-time is further extended to 10 seconds, the same phenomenon occurs, although to a smaller degree.

[0061] Figure 2 shows a current density of 26 A / dm². 2 The relationship between the number of pulses and the amount of deposited chromium is shown for an "on-time" of 1 second and an "off-time" of 10 seconds. The amount of chromium deposited is directly proportional to the number of current pulses. Similar proportional relationships were found for different current density values ​​and combinations of on-time and off-time.

[0062] A comparison of the deposition rates of the electrolyte according to the present invention and commercially available electrolytes shows that the deposition rate obtained by the method of the present invention is much faster. The inventors obtained a maximum deposition rate of 0.40 μm / min. Experiments using commercially available sulfuric acid-based Trylite® Flash SF from MacDermid Enthone were conducted under optimal conditions (deposition temperature 60°C, cathode current density 10 A / dm²). 2, anode current density 3A / dm 2 This demonstrates that a deposition rate of 0.05 μm / min can be obtained at pH 3.7. This electrolyte contains boric acid and a specific compound called Trylite.

[0063] The present invention is further illustrated by the following non-limiting figures.

[0064] Figure 1: Single-pulse electrodeposition process with a pulse width of 1 second as a function of current density. Left side: Chromium deposition amount (mg / m²) 2 ), Right side: Gloss represented by GU (Gloss Unit). Figure 2: Current density 26 A / dm 2 Relationship between the number of pulses and the amount of deposited chromium when the pulse width is 1 second and the interpulse period is 10 seconds. The top line represents ICP-MS measurement, the middle line represents benchtop XRF measurement, and the bottom line represents handheld measurement. Figure 3: Decrease in process efficiency with increasing interpulse duration. S indicates that the Hilan underlying nickel layer was shiny (see Table 3), and D indicates that the underlying nickel layer was dull. 8 and 20 are the 26 A / dm used to deposit the chromium layer. 2 This refers to the number of pulses per second. Figure 4: SEM images of a chromium surface obtained using single-pulse and multi-pulse processes. Both images were created at the same magnification. The measurement bar represents 1 μm. Zeiss instrument: EHT 5.00 kV, Signal A=SE2, Magnification 11430x, Specimen size 10.00 × 7.500 μm 2 The operation was performed using the following parameters: I probe was 150 pA, WD was 4.6 mm, and pixel size was 9766 nm.

Claims

1. A method for electrodepositing a functional or decorative chromium layer onto a metal substrate by a batch or continuous electrodeposition process using an aqueous electrolyte solution that is halide ion-free and borate-free, The aforementioned electrolyte aqueous solution i) A trivalent chromium compound formed by a water-soluble chromium(III) salt, where the electrolyte aqueous solution is 50 mM to 1000 mM Cr ３＋ Contains ions; ii) Sodium sulfate or potassium sulfate in a total amount of 25 to 2800 mM; iii) [Math 1] Formate as a complexing agent with a molar ratio of 1:1 to 4.0:1; iv) Sulfuric acid, sodium hydroxide, or potassium hydroxide to adjust the pH to the desired value; Includes, The pH of the aforementioned electrolyte aqueous solution is 1.50 to 3.00 when measured at 25°C. The temperature of the electrolyte aqueous solution during electrodeposition is 30 to 60°C. The aforementioned metal substrate functions as a cathode, One or more anodes are Cr ３＋ Ion's Cr ６＋ i) a catalytic coating of iridium oxide or ii) a catalytic coating of a mixed metal oxide containing iridium oxide and tantalum oxide, for reducing or eliminating oxidation to ions, A method wherein the electrodeposition is performed by pulsed electrodeposition, wherein the pulsed electrodeposition comprises two or more current pulses performed at a selected current density and a selected pulse width, each current pulse followed by an interpulse period in which the current density is set to zero, the pulse width being at least 0.1 seconds, and the interpulse period being at least 0.1 seconds.

2. The method according to claim 1, wherein the electrolyte aqueous solution further comprises v) a surfactant for promoting the release of hydrogen gas bubbles from the metal substrate.

3. The aforementioned electrolyte aqueous solution i) A trivalent chromium compound formed by a water-soluble chromium(III) salt, where the electrolyte aqueous solution is 50 mM to 1000 mM Cr ３＋ Contains ions; ii) Sodium sulfate or potassium sulfate in a total amount of 25 to 2800 mM; iii) [Math 2] Formate as a complexing agent with a molar ratio of 1:1 to 4.0:1; iv) Sulfuric acid, sodium hydroxide, or potassium hydroxide to adjust the pH to the desired value; vi) The remaining unavoidable impurities It consists of, or i) A trivalent chromium compound formed by a water-soluble chromium(III) salt, wherein the aqueous electrolyte solution contains 50 mM to 1000 mM Cr³⁺ ions; ii) Sodium sulfate or potassium sulfate in a total amount of 25 to 2800 mM; iii) [Math 3] Formate as a complexing agent with a molar ratio of 1:1 to 4.0:1; iv) Sulfuric acid, sodium hydroxide, or potassium hydroxide to adjust the pH to the desired value; v) A surfactant for promoting the release of hydrogen gas bubbles from the metal substrate; vi) The remaining unavoidable impurities The method according to claim 1, comprising:

4. The method according to any one of claims 1 to 3, wherein the pH is adjusted to a value of 2.00 or higher.

5. The method according to claim 4, wherein the pH is adjusted to a value of 2.00 to 2.

75.

6. The method according to any one of claims 1 to 5, wherein the batch or continuous electrodeposition process is a batch electrodeposition process, and in the batch electrodeposition process, the pulse width is 0.5 to 2.5 seconds and the interpulse period is 0.5 to 5 seconds.

7. The method according to any one of claims 1 to 5, wherein the batch or continuous electrodeposition process is a continuous electrodeposition process, and in the continuous electrodeposition process, the pulse width is 0.5 to 2.5 seconds and the interpulse period is 0.5 to 5 seconds.

8. The method according to claim 7, wherein in the continuous electrodeposition process, the pulse width is 0.5 to 2 seconds and the interpulse period is 0.5 to 2 seconds.

9. The method according to any one of claims 1 to 8, wherein the water-soluble chromium(III) salt is basic chromium(III) sulfate and / or the complexing agent is sodium formate.

10. The amount of chromium deposited is at least 1 g / m². ２ The method according to any one of claims 1 to 9.

11. The method according to any one of claims 1 to 10, wherein the temperature of the electrolyte aqueous solution during electrodeposition is at least 35°C.

12. The method according to claim 11, wherein the temperature of the electrolyte aqueous solution during electrodeposition is 35°C to 50°C.

13. The method according to any one of claims 1 to 12, wherein the batch or continuous electrodeposition process is a continuous electrodeposition process, and the line speed of the electrodeposition line in the continuous electrodeposition process is at least 50 m / min.

14. The method according to claim 13, wherein the line speed of the electrodeposition line in the continuous electrodeposition process is at least 100 m / min.

15. The method according to any one of claims 1 to 14, wherein the molar ratio of complexing agent to Cr is 2.0:

1.

16. The method according to any one of claims 1 to 15, wherein the metal substrate is a non-alloy or low-alloy steel strip or sheet.

17. The method according to claim 16, wherein the metal substrate is a nickel-coated steel strip or sheet or a copper-coated steel strip or sheet.

18. The method according to any one of claims 1 to 17 for producing a metal substrate having a functional or decorative chrome layer having a gloss value of at least 800 when measured at an angle of 20° in accordance with ISO 2813:2014.

19. The method according to any one of claims 1 to 17 for manufacturing a metal substrate for use in photovoltaic applications, comprising a functional chromium layer having a thickness of 75 to 1000 nm and having a gloss value of at least 800 when measured at an angle of 20° according to ISO 2813:2014.

20. Use in photovoltaic applications of a coated metal substrate comprising a functional chromium layer having a thickness of 75 to 1000 nm and a gloss value of at least 800 when measured at an angle of 20° according to ISO 2813:2014, manufactured by the method of claim 19.

21. The use according to claim 20, wherein the photovoltaic application is a solar cell.

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