EP3170925A1 - Method for producing a metal surface - Google Patents

Abstract

The invention relates to an economic metallization, in particular of vehicle parts, by Entchromes and a particular nickel layers having subsequent process which allows an adjustable surface finish by combining dull and shiny layers and / or incorporating a mechanical grinding process, the layer structure in connection with the initial Entchrom more commercial chrome plated parts shows a special reliability.

Description

The present invention relates to a method for producing a metal surface on a component which is to have a matted appearance.

Metallic surfaces are desired for many components and are adapted in many ways to the particular technical and aesthetic requirements. This relates to the metallization of already metallic base body but also the metallization of non-metallic components, especially those made of plastic materials. A preferred application in the present context relates to vehicle parts, especially vehicle interior parts and in particular trim parts of a car, especially inside.

The present invention is based on the problem to provide an economical method for producing a metal surface.

• nasschemisches oxidatives Entchromen eines verchromten Werkstücks,
• saure galvanische Nickelbeschichtung der entchromten Oberfläche des Werkstücks und
• weitere Metallisierung der sauer galvanisch nickelbeschichteten Oberfläche des Werkstücks.

This task is solved by the following steps and the following order:

• wet-chemical oxidative descaling of a chromium-plated workpiece,
• Acid nickel plating of the chromium-plated surface of the workpiece and
• further metallization of the acidic galvanic nickel-coated surface of the workpiece.

A basic idea of the invention is to make an already chrome-plated workpiece the starting point of the method. This chrome-plated part is chromium-plated, wet-chemically and oxidatively (in particular anodically), ie by converting the chromium into chromium oxides or chromates. It has been found that in many applications by standard methods chrome-plated workpieces can be obtained at very low cost, because they are produced on an industrial scale and in very large quantities. These workpieces are well protected by chrome plating and easy to transport. They can then be dechromed again for more individualized metallization so that the base metallization underlying the removed chromium layer is available e.g. B. a nickel surface.

However, experience has shown that it is not always easy to rebuild a reliable and good new metallization after dechroming. In this context, it has proven particularly useful to insert an intermediate layer of nickel, which is electrodeposited from an acidic bath. Here, a pH of at most 1 is preferred. Preferably, the ingredient mainly responsible for the acid of the bath is hydrochloric acid, and preferably, the nickel is present in this bath as chloride. The process may conveniently take place at about room temperature, that is, for example, in a temperature range of 10 to 45 ° C, preferably 15 to 40 ° C or 15 to 35 or 30 ° C. The preferred layer thickness is 0.5 μm to 3 μm, preferably up to 2 μm.

This nickel interlayer forms a reliable and with regard to the subsequently desired and to be adjusted gloss or matte as well as very advantageous basis for adhesion.

This is followed by another metallization, which may be, for example, and preferably again a nickel layer, in particular a Watt's nickel layer, which is typically deposited at a higher pH, on the order of pH 4. It can be made from baths with nickel sulfate and also chloride, buffered with boric acid, are deposited.

This results in a microscopically bulbous layered structure in which the tuber sizes and tuber intervals can be set via the current intensity and / or coating time, which ultimately determine dullness. A maximum dullness arises when the tubers are practically close to each other. Current strengths in the range of 0.1 to 2 A / dm ² , better 0.1 to 1 A / dm ² , are preferred here.

The Schickstärke the matte layer should be comparatively low and can be between 1 and 20 microns, with upper limits of 19 microns, 18 microns, 17 microns, 16 microns and more preferably 15 microns and lower limits of 2 microns, 3 microns, 4 microns and more preferably 5 microns are even cheaper. The layer thickness is also determined by optical / aesthetic considerations.

Then a shiny metallization can be deposited, in particular a nickel layer again. Baths that are basically also suitable for the Wattsche nickel layer, but which contain glaze carriers as additives, some saccharin and wetting agent are considered here. Depending on the thickness, such a layer can restore the existing dullness to a certain luster and make the gloss level finely adjustable by virtue of its thickness. So it can, for example, depending on the aesthetic requirements or other criteria, a certain "semi-gloss" set. A favorable thickness for this nickel layer is in the range of 5 and 25 microns, with a lower limit of 10 and an upper limit of 20 microns and 15 microns are more preferred. A protective topcoat is preferred. If the metallic nickel color is of interest, a clearcoat can also be used here.

A particular advantage is that can be adjusted by galvanic parameters in a very simple manner, the degree of gloss or matte degree. Different optical properties can be generated with one and the same basic process, that is, the same solution compositions, identical baths, etc. In particular, can be adjusted from batch to batch simply on the current, or even cheaper over the treatment time, the dullness. The thicker the matt nickel layer is, the higher the degree of matting results.

In addition, this or other metal layer may be mechanically ground to the desired aesthetic image (or other purposes) on the basis discussed (prior to application of the topcoat layer). In particular, the mechanical grinding may be on a part of the surface and other aesthetic (or other) specifications may be observed in another part, for example the adjustable gloss or adjustable dullness just mentioned.

According to a further embodiment, it is additionally provided to produce a matting by mechanical grinding and then to deposit a further metal layer over it. Of course, this additional metal layer is not intended to completely level the matted structure, but at least to a substantial extent. Depending on the individual case, metallization processes tend more or less to flatten roughnesses underneath. The smoothing or leveling to a certain extent may well be desired, so you can also use the leveling effect as a design tool. Accordingly, the layer is to be set thicker or to choose the material of the upper metal layer.

In addition, the materials below and above the ground surface may differ. Then, for example, the appearance of metal color may be determined by the upper metal layer, although it may be less suitable for grinding. Grinding offers a known and proven way of matting the surface with roughness and line geometry that can be set in relatively wide limits in comparison to chemical processes. For example, during grinding, certain types of grinding movements and certain gradations of the abrasive may be selected.

Preferably, abrasives are used which contain abrasive particles, that is to say, in particular, abrasive pastes, particle-coated abrasive papers or abrasive cloths, and, in a particularly preferred manner, bonded abrasive particles in nonwovens or brushes with bristles occupied by corresponding particles. By contrast, less preferred are abrasives without abrasive particles, that is, in particular conventional brushes, for example with metal bristles. They may, the inventors have found, pose cleaning problems and tend to smear.

A preferred size range for the abrasive particles is between 10 .mu.m and 200 .mu.m, the lower limits increasingly being preferred are 20 .mu.m, 30 .mu.m and 35 .mu.m, and the upper limits increasingly preferred are 150 .mu.m, 100 .mu.m, 80 .mu.m, 60 .mu.m and 50 .mu.m. These ranges refer to averages.

The experiences of the inventor have shown that the mechanical grinding of the metallic layers discussed here makes special demands on the quality of the basic structure and the methods according to the invention, in particular with the acidic galvanic intermediate nickel plating, prove particularly suitable.

A particular advantage of matting with mechanical grinding is the possibility of a substantially uniform line direction, so to speak a "brushed" appearance. For this just uniform movements of the abrasive or a rotation of the same to achieve a straight movement along the surface to be ground to perform.

A suitable thickness for the metal layer to be ground can be, for example, at least 5 μm, preferably at least 10 μm.

The metal layer above can contain a metal selected from the group consisting of chromium, silver, gold, copper, one of the platinum metals and nickel as the main constituent or (in the technical sense) exclusively. But it could be used combinations thereof. Particularly preferred are silver, gold, the platinum metals and especially chromium. In principle, and especially in the case of not entirely unproblematic surfaces such as nickel, the metal layer may additionally be coated, preferably transparent for the preservation of the appearance. Uncoated metal layers are preferred. A suitable thickness for the metal layer on the ground surface may, for example, be between 0.1 and 3 μm. To improve a layer of z. B. 1 - 5 microns "semi-gloss" nickel can be applied to the ground surface.

In the following the invention will be explained in more detail with reference to an embodiment.

A commercially available and chromed car interior trim part is procured and anodically removed from the chromium plating in a known strongly oxidizing dechroming.

In particular, the resulting base surface may already be a nickel surface (passivated as a result of the dechroming). This surface is according to the invention in a very acidic nickel chloride bath with hydrochloric acid to adjust a pH of just below 1 relatively thin nickel, z. B. for 15 minutes at room temperature, ie about 18 to 20 ° C, at a typical current density of 0.5 A / dm ² , which gives an approximate layer thickness of 0.5 - 1 micron.

This layer provides an excellent base for a per se known Watt's nickel plating at a pH (boric acid buffering) of about 4, for which a nickel sulphate bath is used, without brightener additives. This is carried out at a current density of about 0.5 A / dm ² from an aqueous solution containing 210 g / l nickel sulfate, 35 g / l nickel chloride and 40 g / l boric acid without further additives. The layer thickness range is between 5 and 15 .mu.m, whereby the mattness of the layer ultimately resulting is adjusted via the layer thickness.

This Wattsche nickel layer is then coated in need to reduce their own dullness with a so-called semi-bright nickel layer, in the z. B. saccharin as a glossy carrier and wetting agent are added to the otherwise unchanged bath (the nickel plating Vernickelung). Depending on the strength of this semi-bright nickel layer, there is often a silk mattness or a limited gloss given off for aesthetic reasons.

This nickel surface is then mechanically ground. For this purpose, commercially available skew products are used which contain plastic-bonded abrasive articles in a nonwoven. Exemplary may be the so-called Scotch-Brite products of the manufacturer 3M. There, the nonwoven fibers form an elastic nonwoven base structure, wherein the abrasive bodies are incorporated in the nonwoven by a resin bond. In this case, it is preferable to work with a predetermined line direction and, for example, with the relatively fine FEPA grain size P320 or P360, which corresponds to a particle size of about 40 to 45 μm. The result is a fine unidirectional line structure that matts the metal layer.

The mentioned abrasive products are available in different packaging. For working by hand flat products are suitable in the manner of a lobe; but it can also be done by machine with belts or rotating cylinders.

Finally, a thin "semi-gloss" nickel layer and then a topcoat are applied first. In this embodiment, this is a conventional gloss chromium layer of thickness 1 micron. Here is the Schlötter-Bad slotochrome GC10 with hexavalent chromium or slotochrome 50 with trivalent chromium into consideration.

Thus, the total layer is well protected against environmental influences and resistant to oxidation. It ultimately shows an adjustable metallic chrome gloss.

If desired, of course, other top coats and thus other colors can be used.

Claims (15)

Method for producing a metal surface with the following steps in the following order: wet-chemical oxidative descaling of a chromium-plated workpiece, - acidic nickel plating of the chromed surface of the workpiece and - Further metallization of the acidic nickel-coated surface of the workpiece. The method of claim 1, wherein the pH of a bath used for the acidic nickel plating is at most 1. A method according to claim 1 or 2, wherein a bath used for the acidic nickel plating contains nickel chloride. Method according to one of the preceding claims, in which a bath used for the acidic nickel plating contains hydrochloric acid as the acid responsible for the acidic adjustment. Method according to one of the preceding claims, in which the acidic nickel plating produces a layer thickness of between 0.5 μm and 3 μm. Method according to one of the preceding claims, in which the further metallization is a nickel coating, in particular the deposition of a nickel-nickel layer. The method of claim 6, wherein the further metallization with the Watt's nickel layer is followed by a shiny metallization, in particular with nickel. Method according to one of the preceding claims, in which the workpiece is mechanically ground after the further metallization on the metallized surface. The method of claim 8, wherein after the mechanical grinding, a further metal layer is deposited, which does not completely level the surface structure of the ground surface. The method of claim 9, wherein the mechanical grinding is carried out using abrasive particles, in particular in a size range between 10 .mu.m and 200 .mu.m of the abrasive particles. The method of claim 10, wherein the abrasive particles are bound in a plastic, in particular by the abrasive particles are incorporated in plastic fibers or bristles of a nonwoven or a brush. Method according to one of claims 8 to 11, wherein after the Entchroming and before the mechanical grinding, a metal layer of a total thickness between 5 .mu.m and 100 .mu.m is deposited. A method according to any one of claims 9 to 12, wherein the further metallization on the ground surface deposits a chromium, silver, gold, copper, platinum metal or nickel layer or a combination thereof. A method according to claim 13, wherein a shiny intermediate nickel layer is deposited on the ground surface prior to further metallization. Method according to one of the preceding claims, in which a vehicle part, in particular a vehicle interior part, in particular an automobile part and in particular an automotive interior part is produced.