EP2743375B1 - Method of coating a component - Google Patents

Description

The present invention relates to a method for coating a carbon fiber reinforced plastic component.

In such components, carbon fibers (hereinafter "carbon fibers") are embedded in a plastic material and mechanically reinforce it; in this way, components can be produced which can be distinguished, for example, by high mechanical strength, in particular by high tensile strength in the direction of the fibers. Due to the mechanical reinforcement through the carbon fibers, the components can also be realized with a reduced weight overall, which can be of interest with regard to lightweight construction applications, which are becoming increasingly important in the course of the increasing requirements for energy efficiency in mobility.

U.S. 2010/304063 A1 relates to a method of making a metal-coated polymeric article comprising providing a polymeric material, an optional intermediate layer, and a metal coating. The polymer article can be a carbon fiber reinforced plastic part and various pickling methods can be used for pre-treatment.

The present invention is based on the object of specifying a particularly advantageous method for coating a plastic component.

• Vorsehen eines Kohlefaser-verstärkten Kunststoffbauteils;
• Vorbehandeln des Bauteils für die Beschichtung, und zwar in gasförmigem Schwefeltrioxid, und anschließend
• Abscheiden der Metallschicht in einem Bad,

wobei das Kohlenstofffaser-verstärkte Kunststoffbauteil vor dem Vorbehandeln in Salpetersäure behandelt wird.According to the invention, this task is solved by a method with the following steps:

• providing a carbon fiber reinforced plastic component;
• Pre-treating the component for coating, namely in gaseous sulfur trioxide, and then
• depositing the metal layer in a bath,

wherein the carbon fiber reinforced plastic component is treated in nitric acid before the pre-treatment.

The deposition of the metal layer can include seeding the component with palladium, for example; For this purpose, the component can (after the pre-treatment) be placed, for example, in an acidic, ionogenic palladium solution, with palladium ions accumulating on the component surface. These can then be converted into palladium nuclei, for example in a reducing bath.

Usually, a metal layer is first deposited electrolessly, ie chemically. The metal is stored, for example chemically deposited nickel, to the palladium nuclei, and an initially thin layer is formed ("seed layer"); this can then be reinforced, preferably galvanically, i.e. electrochemically in a bath. Thus, for example, a nickel layer deposited electrolessly after palladium seeding can be reinforced galvanically, for example by a nickel and/or chromium and/or copper layer.

The metal layer can be deposited "in a bath" in this respect without current (chemically) and/or galvanically; a combination of electroless and galvanic deposition is preferred.

A criterion for assessing the quality of a correspondingly deposited metal layer can be its adhesion to the component. The inventors have found that the adhesion of a metal layer deposited chemically/galvanically on a carbon fiber-reinforced plastic component can be significantly increased by pretreatment in gaseous sulfur trioxide, or that the pretreatment is what makes the deposition of the metal layer possible in the first place; this is surprising insofar as comparative tests with glass fiber reinforced plastic components have often not shown satisfactory results.

The inventors have observed as a possible reason for the good adhesion properties achieved with the method according to the invention that the wetting of the carbon fiber-reinforced plastic components can be improved by treatment in gaseous sulfur trioxide. Also due to the poor adhesion of metal layers experimentally deposited on glass fiber reinforced plastic components with the same pretreatment, it is assumed that there could be a certain interaction between the carbon fibers and the coating of plastic components treated in gaseous sulfur trioxide.

The status of the current investigations is that in the case of a chemical deposition on the carbon fibers, due to their electrical conductivity (albeit possibly only low), metal can also be deposited directly, i.e. possibly without pretreatment; with the treatment in gaseous sulfur trioxide, the plastic material could therefore be prepared for the coating as a matter of priority. In this respect, there seems to be an interaction in that the Carbon fibers close "gaps" in the pretreatment/nucleation of the plastic material, which otherwise (reference tests with glass fiber reinforced plastic components) can result in a metal coating with unsatisfactory adhesion values; on the other hand, the pre-treatment in gaseous sulfur trioxide also closes the "gaps" between the carbon fibers.

Further preferred embodiments can be found in the dependent claims and in the description below.

A period of at least 10 seconds, with increasing preference in this order of at least 20 seconds, 30 seconds, 40 seconds, 50 seconds, has proven particularly suitable for the pretreatment in the gaseous sulfur trioxide, also with a view to the adhesion properties of the subsequently deposited metal layer . Limiting the treatment time is also advantageous with regard to throughput in mass production; possible upper limits are 10 minutes, 9 minutes, 8 minutes, 7 minutes, 6 minutes and 5 minutes, respectively, with increasing preference in this order.

The component is preferably rinsed, particularly preferably with water, immediately after the treatment in the gaseous sulfur trioxide, even before the metal layer is deposited.

Roughening of the surface, for example, can also contribute to the good adhesion properties, which can already occur during the course of the pretreatment in gaseous sulfur trioxide. The roughness is further increased by an additional treatment. According to the invention, the carbon fiber reinforced plastic component is treated in nitric acid before the pretreatment. In a preferred embodiment, the plastic component is additionally sandblasted before the pretreatment in sulfur trioxide.

In a preferred embodiment, the plastic material in which the carbon fibers are embedded is a duroplastic material. The inventors have achieved particularly good results, including the adhesion properties and insofar as the effectiveness of the pretreatment in gaseous sulfur trioxide is concerned, with carbon fibers embedded in a resin; a melamine resin is particularly preferably provided as the matrix material.

The seeding of the component with palladium provided in a preferred embodiment has already been described at the outset; A nickel layer is then particularly preferably chemically deposited and this is then reinforced by a galvanically deposited nickel layer. In the further process, for example, a copper layer can then be deposited in an acidic bright copper process (acidic copper), preferably in several steps, ie in at least two bright copper steps; between the individual bright copper steps, the surface is preferably ground. Then, for example, another layer of nickel can be deposited and brushed to give the surface an attractive aesthetic appearance. Finally, for example, a nickel and/or a chromium layer can then be applied.

The method according to the invention is used to produce a carbon-fiber-reinforced plastic component. Such a component is designed as a component that belongs to the load-bearing structure of a motor vehicle, in particular a passenger car, i.e. as part of the underbody with, for example, an engine mount, side member and cross member (as well as the boot floor and wheel housings); the component coated according to the invention can therefore be part of the side member, for example. The inventors have found that a correspondingly coated component can be characterized by increased mechanical stability, for example by high torsional rigidity; Advantageously, the component can thus be used not only as a decorative covering (which is of course also possible in general, of course), but also as part of the supporting structure. The component can also be part of the body of the motor vehicle.

Preferably, the component (also) provides a visible surface of the motor vehicle interior. Particularly preferably, the component is at the same time part of the supporting structure, which can help to save material, for example because otherwise one component would have to be used as part of the supporting structure and an additional component to cover it; the saving of material can be of interest with a view to an overall light construction. The component can thus, for example, provide a decorative surface for the center console of a passenger car and at the same time be part of the side member.

The use of a component coated according to the invention in the interior of a motor vehicle can also be advantageous in that the well-adhering metal layer can hold the component (or fragments thereof) together in the event of fracture or at least prevent the smallest fragments from splintering. If the component breaks in a traffic accident, for example, the metal layer can reduce the risk of sharp-edged fragments forming.

In this respect, the use of a component coated according to the invention is generally preferred in applications in which, on the one hand, there may be a risk of breakage and, on the other hand, personal contact with fragments cannot be ruled out. In addition to the motor vehicle sector, this can also be the case, for example, with sports equipment and aircraft or watercraft.

A component coated according to the invention preferably has no further coating in addition to the metal coating; in particular, no plastic coating is provided that would otherwise be necessary as protection against splintering, which is also advantageous with regard to an overall cost-effective design and can help to save weight.

The invention is explained in more detail below using a reference example.

To produce a carbon fiber reinforced plastic component, which is designed as part of the side member of a motor vehicle and is later intended to provide a decorative surface in the interior, carbon fiber mats are first pre-soaked in the plastic material, an epoxy resin. The pre-soaked mats are then bonded under pressure in a mold and harden to form the carbon fiber reinforced plastic component.

The surface of the carbon fiber reinforced plastic component to be coated (hereinafter "the component") is first sandblasted and roughened to prepare for the coating.

The component is then pre-treated in gaseous sulfur trioxide for a period of one minute. After rinsing with water, the component is seeded with palladium, i.e. first placed in an ionogenic palladium solution, with palladium ions accumulating on the surface; these then become palladium nuclei in a reducing bath.

Nickel can then accumulate on these palladium nuclei, specifically in the first step of an electroless, i.e. chemical, nickel deposition. In a second step, the electrolessly deposited nickel layer is reinforced with a galvanically deposited nickel layer.

A copper layer (acidic copper) is then applied to the galvanically deposited nickel layer, the component is then ground and then another copper layer (acidic copper) is deposited. The component is then nickel-plated, brushed and finished with a nickel/chrome layer.

Claims (10)

1. Method for coating a carbon fibre-reinforced plastics component with a metal layer, comprising the steps of:

   - providing the carbon fibre-reinforced plastics component,

   - pretreating the component for the coating, specifically in gaseous sulphur trioxide, and then

   - depositing the metal layer in a bath,

   characterised in that the carbon fibre-reinforced plastics component is treated in nitric acid prior to the pretreatment.
2. Method according to claim 1, wherein the carbon fibre-reinforced plastics component is treated in the gaseous sulphur trioxide for a period of at least 10 seconds and at most 10 minutes.
3. Method according to claim 1 or 2, wherein the carbon fibre-reinforced plastics component is rinsed, preferably with water, immediately after treatment in the gaseous sulphur trioxide.
4. Method according to any of the preceding claims, wherein the carbon fibre-reinforced plastics component is sand-blasted prior to the pretreatment.
5. Method according to any of the preceding claims, wherein a plastics material of the carbon fibre-reinforced plastics component, in which plastics material the carbon fibres are embedded, is a duroplastic material, preferably a resin, particularly preferably a melamine resin.
6. Method according to any of the preceding claims, wherein the deposition of the metal layer comprises seeding the component with palladium as a first step.
7. Method according to claim 6, wherein the seeding of the component with palladium comprises treatment firstly in an ionogenic palladium solution and then in a reducing bath.
8. Method according to any of the preceding claims, wherein the deposition of the metal layer takes place electrolessly in a first step and galvanically in a second step.
9. Method according to claim 8, wherein a nickel layer is chemically deposited in the first step.
10. Method according to claim 9, wherein the chemically deposited nickel layer is reinforced by a galvanically deposited nickel layer in the second step.