Patent Application
20240011178
The present invention relates to a black plated substrate comprising a base-substrate and deposited thereon a layer stack, wherein the layer stack comprises a black chromium plating layer comprising on its surface a conversion layer having a depth of 30 nm or more, characterized in that the conversion layer does not comprise metallic chromium or comprises metallic chromium only up to 2 at.-%, based on the element chromium and the total number of chromium atoms in the conversion layer.
From the very beginning of chromium layers an interest in dark chromium layers was observable. Beginning with dark hexavalent chromium layers, the focus today significantly shifted to trivalent chromium layers due to a higher environmental acceptance.
Typically, each chromium layer, in particular dark chromium layers, are characterized by color values referenced to the L*a*b* color-space system. While the value L* defines the brightness (or sometimes also referred to as lightness), values a* and b* define the color of a respective chromium layer. While a L* value of 100 defines a diffuse white, a L* value of 0 is a deep black. Values for a* and b* can be positive and negative, wherein a* values describe the colors green (negative) and red (positive), while b* values describe the colors blue (negative) and yellow (positive). A combination of a* and b* with 0 describes a neutral grey color, turning into a deep neutral black the lower the L* value (e.g. of 50 or below).
Depending on the chemical composition of a respective aqueous trivalent chromium electroplating bath and/or its deposition parameters a huge variety of L*a*b* values can be generated.
Analysis have shown that such deep neutral black colors often come along with a specific surface modification particularly on the outer surface of a respective electroplated black chromium plating layer, sometimes referred to as conversion layer or surface-modified layer.
US 2020/094526 A1 refers to a black plated resin part and method producing the same. It discloses a black chromium plating layer comprising such a surface-modified layer. US'526 discloses that the thickness of the surface-modified layer correlated with the amount of agent M added (see US'526, [0078]) and current density applied (see [0079]). Furthermore, US′526 discloses a thickness of the surface-modified layer up to 37.7 nm (see Sample No. 1).
Own investigations have shown that the long-time stability of the black color is better preserved the higher the thickness of the conversion layer. It is assumed that the wear resistance of the conversion layer increases with an increased thickness of the conversion layer. This means that the black color is longer preserved and protected from e.g. physical contacts, if the layer thickness has at least a sufficient minimum thickness. It is furthermore assumed that with an increased thickness of the conversion layer an increased hardness of this layer is obtained.
Therefore, there is an ongoing demand to provide improved black plated substrates.
It was therefore an objective of the present invention to provide a black plated substrate, which in particular provides a black chromium plated layer comprising a conversion layer with improved color stability and wear resistance, such that an optical impression is maintained for a longer time.
These objectives are solved by the present invention, i.e. by a black plated substrate comprising a base-substrate and deposited thereon a layer stack, wherein the layer stack comprises
In the context of the present invention, emphasis is given on decorative applications. Thus, in the context of the present invention, the black plated substrate and therefore the black chromium plating layer preferably refers to a decorative black plated substrate and a decorative black chromium plating layer, respectively. Thus, the black chromium plating layer is preferably not a black hard chromium plating layer.
Own experiments have shown that an increased thickness of the conversion layer is obtained if in a respective electroplating bath utilized in a respective plating method not only the correct plating additives are used but also in specific amounts (see examples below). It furthermore appears that in such desired black chromium plating layers the amount of metallic chromium in the conversion layer is particularly low, i.e. not exceeding 2 at.-%. As a result thereof, a comparatively increased (and desired) thickness of the conversion layer is obtained resulting in an improved wear and abrasion resistance, respectively. This results in a black plated substrate with increased lifetime regarding the optical black perception.
The black substrate comprises a black chromium plating layer obtained from a plating process, preferably an electrolytic plating process. This includes that the black chromium plating layer is obtained by a wet-chemical plating process. In other words, the black plated substate and the black chromium plating payer, respectively, are not obtained by physical deposition methods, e.g. vapor deposition.
The present invention particularly refers to such a specifically designed black plated substrate with a respective black chromium plating layer comprising a conversion layer as defined above and throughout the present text.
The black plated substrate of the present invention comprises a base-substrate.
Preferred is a black plated substrate of the present invention, wherein the base-substrate comprises, preferably is, a metallic or non-metallic base-substrate, preferably a non-metallic base-substrate, most preferably a plastic base-substrate.
Preferred is a black plated substrate of the present invention, wherein the metallic base-substrate is an iron-comprising metallic base-substrate, preferably an iron base-substrate, most preferably a cast iron base-substrate. Preferably, an iron-comprising metallic base-substrate comprises a brass base-substrate and/or a zinc-based die-cast base-substrate.
Preferred is a black plated substrate of the present invention, wherein the non-metallic base-substrate, preferably the plastic base-substrate, comprises acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene-polycarbonate (ABS-PC), polypropylene (PP), polyamide (PA), polyurethane (PU), polyepoxide (PE), polyacrylate, polyetherimide (PEI), a polyetherketone (PEK), mixtures thereof, and/or composites thereof; preferably acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene-polycarbonate (ABS-PC), polyamide (PA), polyurethane (PU), polyepoxides (PE), polyacrylate, mixtures thereof, and/or composites thereof. Such plastic base-substrates are typically used in decorative applications such as automotive parts, in particular ABS and ABS-PC.
The black plated substrate of the present invention furthermore comprises a layer stack deposited on the base-substrate. The layer stack comprises
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer comprises one or more than one selected from the group consisting of a nickel layer, a nickel alloy layer, a copper layer, and a copper alloy layer. Preferably, they are consecutive; forming a sequence of intermediate plating layers; being adjacent.
More preferably, the layer stack comprises two or more than two intermediate plating layers, most preferably at least one intermediate layer comprising copper and/or a copper alloy and furthermore at least one intermediate layer comprising nickel and/or a nickel alloy.
Thus, preferred is a layer stack comprising more than one intermediate plating layer consecutively following on each other.
In the context of the present invention, the term “plating” denotes a deposition utilizing and not utilizing an external electrical source. Thus, it preferably includes electroplating as well as electroless plating, e.g. electroless plating with the help of a reducing agent.
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer formed on the base-substrate comprises at least one micro-porous nickel-plating layer (sometimes also referred to as MPS nickel-plating layer). Preferably, such a layer comprises non-conductive micro-particles. This most preferably applies, if the base-substrate is a non-metallic base-substrate, preferably a plastic base-substrate. Preferably, this intermediate plating layer, if present, is adjacent to the black chromium plating layer.
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer formed on the base-substrate comprises at least one bright nickel-plating layer or at least one satin nickel-plating layer. This most preferably applies, if the base-substrate is a non-metallic base-substrate, preferably a plastic base-substrate.
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer formed on the base-substrate comprises at least one semi-bright nickel-plating layer. This most preferably applies, if the base-substrate is a non-metallic base-substrate, preferably a plastic base-substrate. More preferred is a black plated substrate of the present invention, wherein said semi-bright nickel-plating layer is present additionally to said bright nickel-plating layer or satin nickel-plating layer.
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer formed on the base-substrate comprises at least one nickel alloy plating layer, preferably adjacent (i.e. directly on) to the base-substrate. This most preferably applies, if the base-substrate is a non-metallic base-substrate, preferably a plastic base-substrate.
Preferred is a black plated substrate of the present invention, wherein the one or more than one intermediate plating layer formed on the base-substrate comprises at least one copper plating layer, preferably adjacent (i.e. directly on) to aforementioned at least one nickel alloy plating layer. This most preferably applies, if the base-substrate is a non-metallic base-substrate, preferably a plastic base-substrate.
Very preferred is a black plated substrate of the present invention comprising
Preferably, features and preferred features regarding the mentioned individual layers apply likewise also the individual layers in this very preferred black plated substrate of the present invention. Furthermore, additional layers in the layer stack, e.g. an activation layer comprising palladium, is not excluded and can be also one of the one or more than one intermediate plating layer.
Preferably, the black chromium plating layer (including the conversion layer) or the passivation layer, if present and deposited on top of the black chromium plating layer, is the outermost layer of the layer stack.
Preferably, the optional passivation layer comprises trivalent chromium phosphate and/or (preferably or) a manganese species. Most preferably, the optional passivation layer has no significant effect on the optical appearance of the black chromium plating layer, most particularly regarding L*, a*, and b* values of the black chromium plating layer.
The layer stack further comprises a black chromium plating layer formed on the one or more than one intermediate plating layer. Generally, a black plated substrate of the present invention is preferred, wherein the black chromium plating layer is adjacent to the outermost intermediate plating layer. The black chromium plating layer is preferably an electroplated black chromium plating layer.
In the context of the present invention, the chromium plating layer is black. This black is preferably optically perceived as a deep dark black. Most preferably, the entire black plated substrate is perceived in this manner.
Most preferred is a black plated substrate of the present invention, wherein the black chromium plating layer is obtained from a trivalent chromium electroplating bath. This means that the source of the chromium in the black chromium plating layer is chromium in its trivalent state and not from hexavalent chromium.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer has a L* value of 53 or less, preferably 51 or less, more preferably 50 or less, even more preferably 49 or less, yet even more preferably 47 or less, most preferably 45 or less, yet even most preferably 43 or less. This most preferably applies likewise to the entire black plated substrate.
More preferred is a black plated substrate of the present invention, wherein the L* value of the black chromium plating layer is ranging from 30 to 55, preferably from 32 to 53, more preferably from 34 to 51, even more preferably from 36 to 49, most preferably from 38 to 47, even most preferably from 40 to 45. This most preferably applies likewise to the entire black plated substrate.
More preferred is an optical perception of a deep dark black with reduced or without any optical perception of another color such as yellowish, brownish, bluish, etc. This means that the deep dark black optical perception is most preferably a neutral dark black optical perception.
Thus, preferred is a black plated substrate of the present invention, wherein the black chromium plating layer has, according to the L*a*b color system, a b* value of +7 or less, of +6 or less, more preferably of +5 or less, even more preferably of +4 or less, most preferably of +3 or less. This most preferably applies likewise to the entire black plated substrate.
More preferred is a black plated substrate of the present invention, wherein the b* value of the black chromium plating layer is ranging from −6 to +6, preferably from −5 to +5, more preferably from −4 to +4, even more preferably from −3 to +3, most preferably from −2 to +2, even most preferably from −1 to +1. This most preferably applies likewise to the entire black plated substrate.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer has, according to the L*a*b color system, an a* value of +5 or less, of +4 or less, more preferably of +3 or less, even more preferably of +2 or less, most preferably of +1 or less. This most preferably applies likewise to the entire black plated substrate.
More preferred is a black plated substrate of the present invention, wherein the a* value of the black chromium plating layer is ranging from −5 to +5, preferably from −4 to +4, more preferably from −3 to +3, most preferably from −2 to +2, even most preferably from −1 to +1. This most preferably applies likewise to the entire black plated substrate.
The black chromium plating layer typically comprises chromium, preferably primarily in a metallic state.
Thus, preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises chromium in a total amount ranging from 20 at.-% to at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 25 at.-% to 63 at.-%, more preferably from 29 at.-% to 56 at.-%, even more preferably from 33 at.-% to 51 at.-%, most preferably from 35 at.-% to 47 at.-%, even most preferably from 38 at.-% to 43 at.-%.
As mentioned above, the source of the chromium in the black chromium plating layer is preferably from chromium in its trivalent state. This typically includes that complexing agents are utilized in a respective electroplating bath in order to complex the respective trivalent chromium ions. Typically, and in contrast to hexavalent chromium sources, this results in a certain carbon content in the black chromium plating layer compared to a chromium plating layer originating from hexavalent chromium sources.
Thus, preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises carbon in a total amount ranging from 5 at.-% to 40 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 6 at.-% to 33 at.-%, more preferably from 7 at.-% to 28 at.-%, even more preferably from 8 at.-% to 24 at.-%, most preferably from 9 at.-% to 20 at.-%, even most preferably from 10 at.-% to 16 at.-%.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises oxygen in a total amount ranging from 12 at.-% to 40 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 14 at.-% to 38 at.-%, more preferably from 16 at.-% to 36 at.-%, even more preferably from 18 at.-% to 34 at.-%, most preferably from 20 at.-% to 31 at.-%, even most preferably from 22 at.-% to 28 at.-%.
In order to obtain the black plated substrate, in particular the black chromium plating layer, preferably blackening agents are typically utilized in a respective electroplating bath for depositing the black chromium plating layer. In some cases, organic and/or inorganic blackening agents are preferred. Very preferred inorganic blackening agents comprise iron-containing compounds, preferably iron ions, most preferably iron (II) ions, cobalt-containing compounds, preferably cobalt ions, most preferably cobalt (II) ions, thiocyanic acid, and/or salts thereof. Preferred organic blackening compounds comprise methionine and/or salts thereof. Preferably, inorganic blackening agents, most preferably said iron-containing and cobalt-containing compounds, are incorporated into the black chromium plating layer.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises iron, preferably in a total amount ranging from 5 at.-% to 23 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 6 at.-% to 21 at.-%, more preferably from 7 at.-% to 19 at.-%, even more preferably from 8 at.-% to 17 at.-%, most preferably from 9 at.-% to 15 at.-%, even most preferably from 10 at.-% to 13 at.-%.
Preferred is a black plated substrate of the present invention, wherein alternatively or additionally to said iron (preferably alternatively), black chromium plating layer comprises cobalt, preferably in a total amount ranging from 5 at.-% to 23 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 6 at.-% to 21 at.-%, more preferably from 7 at.-% to 19 at.-%, even more preferably from 8 at.-% to 17 at.-%, most preferably from 9 at.-% to 15 at.-%, even most preferably from 10 at.-% to 13 at.-%.
Organic blackening agents are typically incorporated into the black chromium plating layer by their sulfur atoms. Thus, preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises sulfur, preferably in a total amount ranging from 0.1 at.-% to 10 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 0.3 at.-% to 9 at.-%, more preferably from 0.5 at.-% to 8 at.-%, even more preferably from 0.7 at.-% to 7 at.-%, most preferably from 1 at.-% to 6 at.-%, even most preferably from 1.3 at.-% to 5 at.-%.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer comprises nitrogen, preferably in a total amount ranging from 0.1 at.-% to 10 at.-%, based on the total amount of atoms in the black chromium plating layer including the conversion layer, preferably from 0.5 at.-% to 9 at.-%, more preferably from 1 at.-% to 8 at.-%, even more preferably from 1.5 at.-% to 7 at.-%, most preferably from 2 at.-% to 6 at.-%, even most preferably from 2.5 at.-% to 5 at.-%.
The black chromium plating layer comprises on its surface a conversion layer. In the context of the present invention, the conversion layer has a depth (or thickness) of at least 30 nm. This is considered to be a useful minimum depth (or thickness) to provide a minimum of a desired wear and abrasion resistance, respectively, to maintain a comparatively long optical lifetime of the black plated substrate.
Preferred is a black plated substrate of the present invention, wherein the conversion layer has a depth of 32 nm or more, preferably of 35 nm or more, more preferably of 38 nm or more, even more preferably of 41 nm or more, yet even more preferably of 44 nm or more, most preferably of 48 nm or more, even most preferably of 51 nm or more.
Preferred is a black plated substrate of the present invention, wherein the conversion layer has a maximum depth of 90 nm or less, preferably of 80 nm or less, more preferably of 70 nm or less, even more preferably of 66 nm or less, yet even more preferably of 62 nm or less, most preferably of 60 nm or less.
More preferred is a black plated substrate of the present invention, wherein the conversion layer has a depth ranging from 30 nm to 90 nm, preferably from 32 nm to 85, more preferably from 35 nm to 80 nm, even more preferably from 38 nm to 70 nm, yet even more preferably from 41 nm to 66 nm, most preferably from 44 nm to 62 nm, even most preferably from 48 nm to 60 nm.
In the black plated substrate, the black chromium plating layer, excluding the conversion layer, preferably has a higher thickness than the depth (or thickness) of the conversion layer. Preferably, the black chromium plating layer, excluding the conversion layer, is at least twice the thickness of the conversion layer, preferably at least 3 times, more preferably at least 4 to 5 times, even more preferably at least 6 to 7 times, most preferably at least 8 to 9 times, even most preferably at least 10 times.
Preferably, depth or thickness of the conversion layer is determined according to B. R. Strohmeier, Surface and Interface Analysis, Volume 15, page 51 to 56, (1990).
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer has a total thickness of 130 nm or more, including said conversion layer, preferably 160 nm or more, more preferably 190 nm or more, even more preferably 220 nm or more, yet even more preferably 250 nm or more, most preferably 275 nm or more, even most preferably 300 nm or more.
More preferred is a black plated substrate of the present invention, wherein the black chromium plating layer has a total thickness ranging from 100 nm to 1000 nm, preferably from 130 nm to 900, more preferably from 160 nm to 800 nm, even more preferably from 190 nm to 700 nm, yet even more preferably from 220 nm to 600 nm, most preferably from 250 nm to 500 nm, even most preferably from 275 nm to 400 nm. Such a total thickness typically provides excellent color stabilities over a typical lifetime of a respective black plated substrate, even if it is regularly touched and/or cleansed by wiping from time to time.
Furthermore, in the context of the present invention, it is desired to have no or only a very little amount of metallic chromium in the conversion layer. It has been shown that the depth of the conversion layer correlates with the amount of metallic chromium in the conversion layer and it appears that the depth is increasing with lowering the amount of metallic chromium. Without wishing to be bound by theory, it appears that this is a result of a combination of specific blackening agents in specific amounts (see examples).
Preferred is a black plated substrate of the present invention, wherein the conversion layer does not comprise metallic chromium or comprises metallic chromium only up to 1.7 at.-%, based on the element chromium and the total number of chromium atoms in the conversion layer; preferably does not comprise metallic chromium or comprises metallic chromium only up to 1.5 at.-%; more preferably does not comprise metallic chromium or comprises metallic chromium only up to 1.2 at.-%, even more preferably does not comprise metallic chromium or comprises metallic chromium only up to 1 at.-%, yet even more preferably does not comprise metallic chromium or comprises metallic chromium only up to 0.8 at.-%, most preferably does not comprise metallic chromium or comprises metallic chromium only up to 0.5 at.-%, yet most preferably does not comprise metallic chromium or comprises metallic chromium only up to 0.3 at.-%.
Besides minimal amounts of metallic chromium (or none thereof), the conversion layer furthermore comprises chromium hydroxide and chromium oxide. Most preferably chromium is only present in the form of metallic chromium up to a maximum of 2 at.-% (including zero at.-%), chromium hydroxide and chromium oxide. Thus, more preferably, the conversion layer consists thereof, based on chromium species in the conversion layer.
Preferred is a black plated substrate of the present invention, wherein the conversion layer comprises chromium in the form of chromium hydroxide, preferably in a total amount ranging from 40 at.-% to 75 at.-%, based on the element chromium and the total number of chromium atoms in the conversion layer, preferably from 46 at.-% to 70 at.-%, more preferably from 50 at.-% to 66 at.-%, most preferably from 54 at.-% to 62 at.-%.
Preferred is a black plated substrate of the present invention, wherein the conversion layer comprises chromium in the form of chromium oxide, preferably in a total amount ranging from 25 at.-% to 55 at.-%, based on the element chromium and the total number of chromium atoms in the conversion layer, preferably from 29 at.-% to 51 at.-%, more preferably from 32 at.-% to 48 at.-%, most preferably from 35 at.-% to 45 at.-%.
More preferably, the conversion layer comprises chromium oxide and chromium hydroxide, wherein the chromium hydroxide has a higher total amount than the chromium oxide. Own experiments have shown that this is as well a very preferred characteristic of the black plated substrate according to the invention (see examples below).
Preferred is a black plated substrate of the present invention, wherein in the conversion layer the atomic ratio of the element chromium to the element oxygen is less than 1 and/or, preferably and, in the black chromium plating layer without the conversion layer the atomic ratio of the element chromium to the element oxygen is more than 1.
In some cases, a black plated substrate of the present invention is preferred, wherein the black chromium plating layer comprises particles, preferably nano particles. Preferred particles comprise one or more than one chemical element selected from the group consisting of silicon, aluminum, and carbon, preferably silicon and aluminum, most preferably aluminum.
Preferably, the particles have a particle size of less than 1000 nm, preferably of less than 500 nm, more preferably at least 90% of the particles have a particle size of less than 500 nm, most preferably at least 90% of the particles have a particle size of less than 150 nm.
Preferably, the particles have an average particle diameter D50 of 100 nm or less, preferably of 80 nm or less, more preferably of 60 nm or less, even more preferably of nm or less, most preferably of 40 nm or less, very most preferably of 30 nm or less, even most preferably of 25 nm or less, based on volume.
Most preferably, the particles comprise aluminum oxide, preferably are aluminum oxide particles.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer is substantially free of, preferably does not comprise, zinc. More preferably, the entire layer stack is substantially free of, preferably does not comprise, zinc.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer is substantially free of, preferably does not comprise, fluorine.
More preferably, the entire layer stack is substantially free of, preferably does not comprise, fluorine.
Preferred is a black plated substrate of the present invention, wherein the black chromium plating layer is substantially free of, preferably does not comprise, aluminum. More preferably, the entire layer stack is substantially free of, preferably does not comprise, aluminum.
The spirit of the present invention is further illustrated in the following examples without limiting the scope of the invention as herein defined in the claims.
As substrates, ABS plaques were used which prior to deposition of the black chromium plating layer were pre-treated as follows:
In a first step, the ABS plaques were cleaned with Uniclean® 151 (product of Atotech) for 5 minutes at 50° C.
In a second step, the cleaned substrates were subjected to a chromo-sulfuric acid etch for about 10 minutes at about 70° C. In a subsequent step, the etched substrates were activated with the help of colloidal palladium.
In a third step, the activated substrates were subjected to an electroless nickel plating step (10 minutes, 40° C.), followed by a 10 vol.-% sulfuric acid dipping step and an electroless copper plating step.
In a fourth step, the copper plated substrates were furthermore subjected to an electrolytic copper plating step (25° C., 50 minutes, 4 A/dm2).
In a fifth step, the electrolytically copper plated substrates were subjected to a semi-bright nickel plating step (55° C., 15 minutes, 4 A/dm2), followed by a bright nickel plating step (55° C., 25 minutes, 4 A/dm2).
In a sixth step, bright nickel plated substrates were subjected to a micro-porous nickel layer plating step (55° C., 4 minutes, 3 A/dm2).
In a seventh step, the following aqueous (i.e. only solvent was water) trivalent chromium electroplating bath was used for depositing a black chromium plating layer:
The electroplating baths further comprised small amounts (up to 4 g/L) of saccharin and between 5 g/L and 50 g/L of a S-containing diol.
The pH value was adjusted to 3.2.
In a subsequent step, electroplating was carried out for about 3 minutes and with a current density of about 10 A/dm2. The temperature of the respective electroplating bath was about 35° C. Agitation was achieved via air agitation. As a result, homogeneously distributed black chromium plating layers were deposited.
Furthermore, the substrates plated with the black chromium plating layer were subjected to a passivation composition comprising permanganate.
In an eighth step, the substrates were immersed into hot water (80° C.) in a rinse step for minutes. This was applied to example E and CE1, wherein for example CE2 no such immersion was carried out.
Afterwards, L*a*b* values, according to the L*a*b* color-space system, were determined (Konica Minolta CM-700 D spectrophotometer; CIE standard illuminator D65 and 10° standard observer). Calibration of the spectrophotometer was done with black and white standards.
Furthermore, HAXPES measurements carried out at the BESSY synchrotron, Berlin, were carried out (photon energy: 6000 eV; Analyzer: ScientaOmicron EW4000; peak resolution was performed as outlined in US 2020/094526 A1, [0070]). The results are summarized in Table 1 below.
In Table 1, “E” refers to examples according to the invention, wherein “CE” refers to comparative examples.
Table 1 shows that a decreasing overall content of methionine and potassium thiocyanate (from 435 mmol/L for E to 251 mmol/L for CE2) results in a correspondingly decreasing layer thickness of the conversion layer (from 55 nm for E to 25 nm of CE2).
In contrast thereto, an increase of the relative amount of chromium metal results in a decreased layer thickness of the conversion layer.
Comparative example CE2 was not subjected to the immersion into hot water at 80° C., wherein comparative example CE1 was. As seen from Table 1, it is mainly the combined total amount of methionine and potassium thiocyanate seemingly having a significant effect on the conversion layer thickness.
Furthermore, only example E according to the invention shows a higher relative total amount of chromium hydroxide than chromium oxide.
As a result, the examples above indicate that a particularly high conversion layer thickness correlates with a significantly low amount of chromium metal in the conversion layer.
In a further test, the black chromium plating layer of example E, subjected to intensive cleaning, was protected longer against undesired abrasion and therefore dark color stability was better than for the black chromium plating layers of comparative examples CE1 and CE2. It was observed that a brighter black color appeared under the conversion layer if the conversion layer was at least almost removed from the black chromium plating layer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20213572.9 | Dec 2020 | EP | regional |
| 20213575.2 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/085219 | 12/10/2021 | WO |
