EP3604623A1 - Method for producing a metal surface - Google Patents

Abstract

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

Description

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

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

The present invention is based on the problem of specifying 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 sequence:

• wet chemical oxidizing chrome plating of a chrome-plated workpiece,
• acidic galvanic nickel coating of the chromed surface of the workpiece and
• further metallization of the acid, electroplated, nickel-coated surface of the workpiece.

A basic idea of the invention is to make an already chromed workpiece the starting point of the method. This chrome-plated part is chrome-plated, namely wet-chemically and oxidatively (in particular anodically), ie by converting the chrome into chrome oxides or chromates. It has been shown that in many applications, chromium-plated workpieces can be procured at very low costs using standard processes because they are large-scale and be produced in very large numbers. These workpieces are well protected by the chrome plating and can be easily transported. They can then be chrome-plated again for a more individual metallization, so that the base metallization underneath the removed chrome layer is available e.g. B. a nickel surface.

However, experience has shown that it is not always unproblematic to rebuild a reliable and good new metallization after de-chrome plating. In this context, it has proven particularly useful to insert an intermediate layer made of nickel, which is electrodeposited from an acid bath. A pH of at most 1 is preferred. The ingredient which is mainly responsible for the acidity of the bath is preferably hydrochloric acid and the nickel in this bath is preferably present as chloride. The process can advantageously take place approximately at room temperature, for example in a temperature interval 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 intermediate layer forms a reliable basis which is very advantageous with regard to the subsequently desired and to be set degrees of gloss or mattness and with regard to liability.

This is followed by a further metallization, which can, for example, and preferably again be a nickel layer, in particular a Watts nickel layer, which is typically deposited at a higher pH, approximately in the order of pH 4. It can be obtained from baths with nickel sulfate and -chloride, buffered with boric acid, can also be separated.

This creates a microscopic tuber-like layer structure in which the tuber sizes and tuber spacing, which ultimately determine the mattness, can be set via the current intensity and / or coating time. Maximum mattness occurs when the tubers are practically tightly spaced. Here are Current strengths in the range from 0.1 to 2 A / dm ² , more preferably 0.1 to 1 A / dm ² , are preferred. The thickness of the matt layer should be comparatively low and can be between 1 and 20 µm, with upper limits of 19 µm, 18 µm, 17 µm, 16 µm and particularly preferably 15 µm and lower limits of 2 µm, 3 µm, 4 µm and particularly preferred 5 microns are even cheaper. The layer thickness is also determined from an optical / aesthetic point of view.

A shiny metallization can be deposited thereon, in particular a nickel layer again. Baths are considered here, which in principle also come into consideration for the Watts nickel layer, but contain gloss carriers as additives, some saccharin and wetting agent. Depending on its thickness, such a layer can convert the existing mattness back into a certain gloss and, thanks to its thickness, make the gloss level finely adjustable. For example, depending on aesthetic requirements or other criteria, a certain "semi-gloss" can be set. A favorable thickness for this nickel layer is in the range of 5 and 25 μm, a lower limit of 10 and an upper limit of 20 μm and 15 μm being more preferred. A protective finishing layer is preferred. If the metallic nickel color is of interest, a clear coat can also be used here.

A particular advantage is that the degree of gloss or mattness can be set in a very simple manner by means of galvanic parameters. Different optical properties can be generated with one and the same basic process, i.e. constant solution compositions, identical baths, etc. In particular, the mattness can be set from batch to batch simply by means of the current intensity or, even more favorably, via the treatment time. The thicker the matt nickel layer, the higher the degree of mattness.

In addition, this or another metal layer can be mechanically ground on the basis discussed (before applying the finishing layer) in order to achieve a certain aesthetic image (or for other purposes).

In particular, mechanical grinding can be limited to one part of the surface and other aesthetic (or other) specifications can be observed in another part, for example the adjustable gloss or the adjustable mattness 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. This additional metal layer should of course not completely level the matted structure, but should at least retain it to a substantial extent. Depending on the individual case, metallization processes tend to level roughness below it. The smoothing or leveling to a certain extent can also be desired, so you can also use the leveling effect as a design tool. Accordingly, the layer must be set thicker or the material of the upper metal layer selected.

In addition, the materials below and above the ground surface can differ. Then, for example, the appearance with regard to metal color can be determined by the upper metal layer, although this may be less suitable for grinding. Grinding offers a known and proven possibility of matting the surface with a roughness and line geometry that can be set within relatively wide limits in relation to chemical processes. When grinding, for example, certain forms of grinding movement and certain gradations of the abrasive can be selected.

Abrasives containing abrasive particles, in particular abrasive pastes, particle-coated abrasive papers or abrasive cloth, and, in a particularly preferred manner, abrasive particles bonded in plastics in fleeces or brushes with bristles with corresponding particles are preferably used. In contrast, less preferred are abrasives without abrasive particles, in particular classic brushes, for example with metal bristles. According to the inventors, they can pose cleaning problems and tend to smear.

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

The experience of the inventor has shown that the mechanical grinding of the metallic layers discussed here places particular 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 successful.

A particular advantage of matting with mechanical grinding lies in the possibility of an essentially uniform line direction, that is to say a "brushed" appearance. For this purpose, uniform movements of the abrasive or a rotation of the same have to be carried out in order to achieve a straight movement along the surface to be ground.

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 chrome, silver, gold, copper, one of the platinum metals and nickel as the main component or (in the technical sense) exclusively. However, combinations of these can be used. Silver, gold, the platinum metals and especially chrome are particularly preferred. Basically, and especially in the case of not entirely unproblematic surfaces such as nickel, the metal layer can also be additionally coated, preferably in a transparent manner to preserve the appearance. Uncoated metal layers are preferred. A suitable thickness for the metal layer on the ground surface can be, for example, between 0.1 and 3 μm. To improve a layer of z. B. 1-5 µm "semi-gloss" nickel can be applied to the ground surface.

The invention is explained in more detail below using an exemplary embodiment.

A commercially available and chromed passenger car interior trim part is procured and anodically freed from the chromium plating in a strongly oxidizing chromium plating bath known per se.

The resulting base surface can in particular already be a nickel surface (passivated as a result of the de-chrome plating). This surface is nickel-plated according to the invention in a very acidic nickel chloride bath with hydrochloric acid to set a pH of just below 1, for example relatively thin. 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 µm.

This layer provides an excellent basis for a well-known Watts nickel plating at a pH (boric acid buffering) of approximately 4, for which a nickel sulfate bath is used, without any additions of gloss. This takes place at a current density of approximately 0.5 A / dm ² from an aqueous solution with 210 g / l nickel sulfate, 35 g / l nickel chloride and 40 g / l boric acid without further additives. The layer thickness range here is between 5 and 15 µm, the mattness of the ultimately resulting layer being adjusted via the layer thickness.

This Wattsche nickel layer is then coated if necessary to reduce its own mattness with a so-called semi-gloss nickel layer, in which, for. B. saccharin as a brightener and wetting agent are added to the otherwise unchanged bath (the Watts nickel plating). Depending on the thickness of this semi-gloss nickel layer, a silk mattness or a limited gloss is often given for aesthetic reasons.

This nickel surface is then ground mechanically. Commercially available oblique products are used for this, the plastic-bonded abrasives contained in a fleece. As an example, reference can be made to the so-called Scotch-Brite products from the manufacturer 3M. There the nonwoven fibers form an elastic nonwoven basic structure, the abrasive bodies being incorporated in the nonwoven by a resin bond. This is preferably done with a predetermined line direction and, for example, with the relatively fine FEPA grit P320 or P360, which corresponds to an abrasive particle size of approximately 40 to 45 μm. The result is a fine unidirectional line structure that mattifies the metal layer.

The abrasive products mentioned are available in different configurations. Flat products in the manner of a cloth are suitable for working with the hand; but it can also be worked mechanically with belts or rotating cylinders.

Finally, a thin "semi-gloss" nickel layer is applied first, and then a finishing layer. In this embodiment, it is a usual glossy chrome layer of 1 micron thickness. The Schlötter Bad Slotochrom GC10 with hexavalent chrome or Slotochrom 50 with trivalent chrome comes into consideration here.

The entire layer is thus well protected against environmental influences and resistant to oxidation. Ultimately, it shows an adjustable metallic chrome gloss.

Of course, other finishing layers and thus other colors can be used if desired.

Claims (14)

Method for producing a metal surface, with the following steps in the following order: - wet chemical oxidizing chrome plating of a chrome-plated workpiece, - Acidic nickel plating of the chromed surface of the workpiece and further metallization of the acidic, galvanically nickel-coated surface of the workpiece, characterized in that the workpiece is mechanically ground on the metallized surface after further metallization. Method according to Claim 1, in which, after mechanical grinding, a further metal layer is deposited which does not completely level the surface structure of the ground surface. Method according to Claim 2, in which the mechanical grinding is carried out using grinding particles, in particular in a size range between 10 µm and 200 µm of the grinding particles. Method according to Claim 3, in which the abrasive particles are bound in a plastic, in particular in that the abrasive particles are bound in plastic fibers or bristles of a nonwoven or a brush. Method according to one of the preceding claims, in which a metal layer with a total thickness between 5 µm and 100 µm is deposited after the de-chrome plating and before the mechanical grinding. Method according to one of claims 2 to 5, wherein the further metallization on the ground surface is a chrome, silver, gold, copper, Deposits platinum metal or nickel layer or a combination thereof. Method according to claim 6, in which a shiny nickel intermediate layer is deposited on the ground surface before further metallization. Method according to one of the preceding claims, in which the pH of a bath used for the acidic galvanic nickel coating is at most 1. Method according to one of the preceding claims, in which a bath used for the acidic galvanic nickel coating contains nickel chloride. Method according to one of the preceding claims, in which a bath used for the acidic galvanic nickel coating contains hydrochloric acid as the acid which is decisive for the acidic setting. Method according to one of the preceding claims, in which the acidic galvanic nickel coating produces a layer thickness 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 Watt nickel layer. Method according to Claim 12, in which the further metallization with the Watts nickel layer is followed by a shiny metallization, in particular with nickel. 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 automobile interior part, is produced.