EP3329036A1

EP3329036A1 - Process for metallizing plastic surfaces

Info

Publication number: EP3329036A1
Application number: EP16742269.0A
Authority: EP
Inventors: Axel Kirste; Tobias Urban; Fabio Nicolini; Simone LUTTER; Frank Richter; Andre CEZANNE
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2015-07-30
Filing date: 2016-07-21
Publication date: 2018-06-06
Also published as: CN107923043A; WO2017016965A1; US20180202048A1; JP2018523016A; KR20180034611A

Abstract

The invention relates to a process for coating plastic surfaces with metals, especially plastic surfaces composed of acrylonitrile/butadiene/styrene copolymers (ABS) and composed of mixtures of these copolymers with other plastics (ABS blends), using an etch solution (composition C) comprising at least one ionic liquid IL, wherein the process comprises the treating of the plastic surface after the etching with an aqueous rinse solution RS while applying ultrasound.

Description

Process for metallizing plastic surfaces Description

The invention relates to a process for coating plastic surfaces with metals, especially plastic surfaces composed of acrylonitrile/butadiene/styrene copolymers (ABS) and composed of mixtures of these copolymers with other plastics (ABS blends), using an etch solution

(composition C) comprising at least one ionic liquid IL, wherein the process comprises the treating of the plastic surface after the etching with an aqueous rinse solution RS while applying ultrasound.

The coating of the surfaces of plastic parts with metals, also called plastic galvanizing, is becoming increasingly important. By plastic galvanizing methods, composite materials which combine advantages of plastics and metals are obtained. Plastic can be converted to virtually any desired shape by simple processing methods such as injection molding or extrusion. In addition, the use of plastic components can achieve a distinct reduction in weight in comparison to metal parts. Subsequent galvanization of the resultant plastic moldings is often conducted for decorative purposes or else to achieve shielding effects.

For example, sanitary fittings, automobile accessories, furniture hardware, costume jewellery and buttons/knobs are metallized either all over or else only partly, in order to impart an attractive appearance to the parts. In addition, plastics can also be metallized for functional reasons. For example, housings of electrical appliances are metallized in order to shield them from emission or immission of electromagnetic radiation. In addition, the surface properties of plastic parts can be altered in a controlled manner via metallic coatings. In very many cases, copolymers of acrylonitrile, butadiene and styrene (ABS copolymers) and mixtures of these copolymers with other polymers are used, for example blends of ABS and polycarbonate (ABS/PC blends).

For production of metallic coatings on plastic parts, the latter are usually secured in frames and contacted with a plurality of different treatment fluids in a particular process sequence. In a first step, for this purpose, the plastics are typically pretreated in order to remove impurities such as greases from the surface. Subsequently, etching methods are usually used to roughen the surface, such that the subsequent metal layers adhere with sufficient firmness. In the etching operation, the formation of a defined homogeneous structure in the form of recesses on the plastic surface is particularly crucial. Thereafter, the roughened surface is treated with what are called activators in order to form a catalytic surface for a subsequent chemical metallization. For this purpose, it is often the case that either what are called ionogenic activators or colloidal systems are used.

"Kunststoffmetallisierung", Handbuch fur Theorie und Praxis ["Plastic Metallization", Handbook for Theory and Practice] (Eugen G. Leuze Verlag, Saulgau, 1991 , pages 46-47) states, for example, that plastic surfaces, for activation with ionogenic systems, are first treated with tin(ll) ions, giving rise to firmly adhering gels of tin oxide hydrate after the treatment and rinsing with water. In the subsequent treatment with a palladium salt solution, palladium nuclei are formed on the surface through redox reaction with the tin(ll) species, these being catalytic for the chemical metallization. For activation with colloidal systems, generally colloidal palladium solutions are used, formed by reaction of palladium chloride with tin(ll) chloride in the presence of excess hydrochloric acid (Annual Book of ASTM Standard, Vol. 02.05 "Metallic and Inorganic Coatings; Metal Powders, Sintered P/M Structural Parts", Designation: B727-83, Standard Practice for Preparation of Plastic Materials for Electroplating, 1995, pages 446-450).

After the activation, the plastic parts are typically first chemically metallized, using a metastable solution of a metallization bath. These baths generally comprise the metal to be deposited in the form of salts in an aqueous solution and a reducing agent for the metal salt. Only when the chemical metallization baths come into contact with the metal nuclei on the plastic surface, for example with the palladium seeds, is metal formed by reduction, which is deposited on the surface as a firmly adhering layer. Often deposited in the chemical metallization step are copper, nickel or a nickel alloy with phosphorus and/or boron.

It is then possible to electrolytically deposit further metal layers onto the plastic surfaces coated with the aid of the chemical metallization bath. It is often the case that there is first an electrolytic deposition of copper layers or further nickel layers before the desired decorative chromium layer is applied electrochemically.

A critical process step in plastic galvanizing is the pretreatment of the plastic surface. One reason why a pretreatment is necessary is to improve, and typically to actually enable, the adhesion of the metal on the plastic surface. For this purpose, the plastic surface is roughened and should obtain more hydrophilic properties. In this context, the formation of a defined homogeneous structure in the form of recesses on the plastic surface is particularly crucial. These recesses serve, in the later metallization steps, as the starting point for the growth of the metal nuclei.

Since roughening has also been conducted by mechanical methods at an earlier stage, swelling and etching of the plastic surface with chemicals has nowadays become established for this purpose. The most commonly used etchant is the chromium-sulfuric acid etchant (chromium trioxide in sulfuric acid), especially for ABS (acrylonitrile-butadiene-styrene copolymer) or else polycarbonate. Chromium-sulfuric acid etchant is very toxic and requires special precautions in the process procedure, aftertreatment and disposal. Because of chemical processes in the etching process, for example the reduction of the chromium compound used, the chromium- sulfuric acid etchant is used up and is generally not reusable.

A process for chemical metallizing of plastic surfaces using a chromium-containing etch solution is described, for example, in DE-A 100 54 544. Also known is the use of ionic liquids for pretreatment (etching) of plastic surfaces in the context of a metallization. WO 2010/142567 describes a process for coating plastics with metal, wherein the plastics are pretreated with a composition comprising at least one salt having a melting point of less than 100°C at 1 bar (ionic liquid). The pretreatment of various thermoplastics is described, for example polyamides, polyolefins, polyesters, polyethers, polystyrene and copolymers of styrene, for example acrylonitrile/butadiene/styrene copolymer (ABS).

Ionic liquids have been known since the end of the forties. They are fluid salt melts which are liquid below 100°C, preferably at room temperature (25°C, 1 bar) and especially at

temperatures below room temperature. Ionic liquids are a novel class of solvents having nonmolecular, ionic character.

Typical cation/anion combinations which lead to ionic liquids are, for example,

dialkylimidazolium, pyridinium, ammonium and phosphonium with halide, tetrafluoroborate, methylsulfate. In addition, there are many further conceivable combinations of cations and anions that lead to low-melting salts.

The use of ionic liquids in a wide variety of different technical fields is known. In connection with polymers, use of ionic liquids as antistats or else as plasticizers has been described in the prior art, for example in WO 2004/005391 , WO 2007/090755 and WO 2008/006422. Document DE 10 2009 003 01 1 discloses the use of ionic liquids as adhesives for polymers.

It is an object of the present invention to provide an improved process for coating plastic surfaces with metals, using ionic liquids in the pretreatment of the plastic part. It is possible to dispense with the hitherto customary use of the toxic and disadvantageous chromium- containing etch solutions. An improvement in the coating process may lie firstly in improved strength/adhesion on the plastic surface and the nature of the metal layer surface, and also in an improvement from a process technology point of view, such as lower entrainment of the etch solution. The process was to be implementable in a very simple and inexpensive manner, and recovery and/or recycling of the etch solution was to be implementable in a very effective manner.

It has been found that, surprisingly, a rinse step using ultrasound after the treatment of the plastic surface with the etch solution comprising at least one ionic liquid can achieve an improved metal coating. The ultrasound rinse step of the invention with an aqueous rinse solution can give a homogeneous, shiny, defect-free and very well-adhering metal surface. More particularly, by means of the process of the invention, it is possible to obtain

advantageous metal coatings having the layer sequence of chemically deposited nickel, copper, nickel, chromium.

The present invention relates to a process for coating plastic surfaces, especially plastic moldings, with metals, comprising the steps of a) pretreating the plastic surface, especially the plastic molding, with a composition C (etch solution) comprising at least one ionic liquid IL; b) treating the plastic surface, especially the plastic molding, from step a) with an

aqueous rinse solution RS while applying ultrasound; c) treating the plastic surface, especially the plastic molding, from step b) with an

activator composition A comprising at least one ionogenic and/or colloidal activator, especially at least one palladium component P, preferably at least one colloidal palladium component P; d) treating the plastic surface, especially the plastic molding, from step c) with an

accelerator composition B comprising an acid and/or a reducing agent; chemically depositing a metal layer, preferably a metal layer consisting essentially of nickel, copper, chromium or alloys thereof, by treating the surface from step d) with a coating composition M1 comprising at least one metal salt, preferably at least one metal salt selected from nickel, copper and chromium salts, and at least one reducing agent, preferably an in situ reducing agent; electrochemically coating the surface, especially the plastic molding, from step e) with at least one further metal layer, preferably a metal layer consisting essentially of copper and/or a metal layer consisting essentially of chromium, by electrochemically treating the surface, especially the plastic molding, from step e) with at least one coating composition M' comprising at least one metal compound, especially at least one metal salt, preferably at least one copper salt, a chromium salt and/or chromic acid.

Compared to the known use of ionic liquids, it is possible to achieve a further distinct improvement in the coating outcome, such as better adhesion of the subsequent metal layers on the plastic surface. It has been found that the ultrasound rinse step can particularly advantageously detach partly dissolved plastic particles from the surface, which leads to more homogeneous structuring of the surface and improved subsequent metal coating. A standard definition of ionic liquids delimits them from the known salt melts by a melting point of below 100°C, preferably below 80°C, or else even below room temperature. In the context of this application, ionic liquids shall be understood to mean those salts which, in the pure state, have a melting point of less than 100°C at 1 bar. It is a feature of the process of the invention that, compared to a conventional rinse step with water, a more homogeneous and better-adhering metal coating is obtained. Preferably, all the metal layers, especially the metal layers of the layer sequence of chemically deposited nickel, copper, nickel and chromium, have advantageous properties. In addition, the water

consumption in the rinse step can be reduced.

It is additionally advantageous that, in the process of the invention, the plastic surface is etched without metal salts, and it is possible to dispense with the use of the toxic and disadvantageous chromium-containing etch solutions.

Plastics and metals

In the context of the present invention, a molding or a plastic molding refers to an article that has originated from a primary forming method, for example an article consisting essentially of plastic that has originated by primary forming methods, for example casting, die casting, injection molding, extrusion blow molding, extrusion, sintering, and optionally a subsequent forming method. This encompasses especially workpieces and semifinished products, for example a formed workpiece, an injection-molded workpiece, a film or a foil.

In the process of the invention, plastics, especially plastics having a nonconductive surface, are coated with a metal in a plurality of steps. They are preferably thermoplastics. Thermoplastics can be melted and converted to the desired shape by different methods, for example injection molding, extrusion, thermoforming or blow molding.

Suitable thermoplastics include polyamides, polyolefins, polyesters, polyethers, polyacetals, especially polyoxymethylene, polycarbonates, polyurethanes, polyacrylates, polystyrenes or copolymers of styrene, especially styrene/acrylonitrile copolymers (SAN), acrylic

ester/styrene/acrylonitrile copolymers (ASA) and acrylonitrile/butadiene/styrene copolymers (ABS).

Polyamides include polycondensates of aminocarboxylic acids, for example of 6- aminocarboxylic acid or epsilon-caprolactam, or polycondensates of diamino compounds and dicarboxylic acids, for example of hexane-1 ,6-diamine and adipic acid.

Suitable polyolefins are polyethylene, polypropylene and copolymers of ethylene or propylene. Suitable polyesters are polycondensation products of polyhydric alcohols, for example butanediol, hexanediol, glycerol or trimethylolpropane, and polybasic carboxylic acids, especially phthalic acid and isomers thereof, adipic acid or trimellitic anhydride.

A particular polyacetal is polyoxymethylene (POM).

Polycarbonates are esters of carbonic acid and polyhydric alcohols, for example bisphenol A; also mentioned are polyestercarbonates comprising further polybasic carboxylic acids as formation components. Typically, polyethers comprise recurrent ether groups. Of particular industrial significance are, for example, polyetherimides especially comprising aromatic ring systems joined via recurrent ether and imide groups, polyether ketones especially comprising phenylene groups joined by recurrent ether and ketone groups, polyether sulfides comprising ether and thioether groups in their polymer backbone, and polyether sulfones comprising recurrent ether groups and sulfone groups in their polymer backbone.

Polyurethanes are typical polyadducts formed from polyfunctional isocyanates and polyhydric alcohols, useful examples being both aliphatic and aromatic compounds. Polyacrylates are homo- or copolymers of acrylic monomers or methacrylic monomers; a particular example is polymethylmethacrylate (PMMA).

It is also possible to carry out the process of the invention, wherein the plastic comprises (or consist of) an carbon-fibre-reinforced epoxy resin. Carbon-fibre-reinforced epoxy resins are commonly known and typically comprises 10 to 90 %, preferably about 50 to 70 % by volume, reinforcing carbon-fibre. Suitable epoxy resins are polyethers which are obtained by reaction of an compound having hydroxyl groups, e.g. bisphenol, with an epoxy compound, e.g. epichloro- hydrine. Typically, epoxy resins may be cured by reaction with an hardener, e.g. amines, acids, acid anhydrides, thiols.

Preferred polymers are homo- and copolymers of styrene, such as polystyrene,

styrene/acrylonitrile copolymer and especially acrylonitrile/butadiene/styrene copolymers (ABS). A preferred embodiment relates to the process of the invention described, wherein the plastic surface is one consisting of or comprising polyamides, polyolefins, polyesters, polyethers, polyacetals, polycarbonate, polyurethanes, polyacrylates, polystyrene or copolymers of styrene selected from styrene/acrylonitrile copolymers (SAN), acrylic ester/styrene/acrylonitrile copolymers (ASA) and acrylonitrile/butadiene/styrene copolymers (ABS). The plastic to be coated may also comprise blends consisting of two or more of the plastics mentioned and/or a plastic part consisting of two or more of the plastics mentioned (two-component plastics).

A further preferred embodiment relates to the process of the invention described, wherein the plastic comprises (or consists of) one or more of plastics selected from polyamides, polyolefins, polyesters, polyethers, polyacetals, polycarbonate, polyurethanes, polyacrylates, polystyrene or copolymers of styrene selected from styrene/acrylonitrile copolymers (SAN), acrylic ester/styrene/acrylonitrile copolymers (ASA), acrylonitrile/butadiene/styrene copolymers (ABS) and carbon-fibre-reinforced epoxy resins. A preferred embodiment relates to the process of the invention described, wherein the plastic surface is one consisting of or comprising polyamides, polystyrenes or copolymers of styrene selected from styrene/acrylonitrile copolymers (SAN), acrylic ester/styrene/acrylonitrile copolymers (ASA) and acrylonitrile/butadiene/styrene copolymers (ABS), or blends and/or multicomponent plastics comprising at least one, preferably at least two, of the plastics mentioned.

Particularly preferred plastics are polyamides and ABS. Most preferably, the plastic comprises acrylonitrile/butadiene/styrene copolymer (ABS) or a blend, for example ABS/PC

(acrylonitrile/butadiene/styrene copolymer and polycarbonate) and/or multicomponent plastic comprising ABS. ABS is supplied, for example, under the Terluran® trade name by Styrolution.

The articles to be coated may consist entirely of one or more of the above plastics. Articles of this kind may have any desired shape and are obtainable, for example, by thermoplastic forming methods such as injection molding, extrusion, thermoforming and blow molding.

Alternatively, they may consist of different materials. What is essential is that the surface to be coated consists of plastic. In the process of the invention, the plastic or the plastic surface is coated with metals. Useful metals are especially nickel, aluminium, copper, chromium, tin or zinc and alloys thereof. The metal may be applied in one or preferably in more than one layer or operation. It is possible with preference to apply layers of different metals, especially at least three different metal layers. A preferred embodiment relates to the process of the invention described, wherein the metals comprise at least one metal selected from nickel, aluminium, copper, chromium, tin, zinc and alloys thereof.

Ionic liquid IL

The composition C used in the process of the invention comprises at least one salt having a melting point of less than 100°C at 1 bar (called ionic liquid IL hereinafter). Preferably, the ionic liquid IL has a melting point of less than 100°C, more preferably less than 85°C and most preferably less than 60°C, in each case at 1 bar (standard conditions).

The molar mass of the ionic liquid IL is preferably less than 2000 g/mol, more preferably less than 1500 g/mol, more preferably less than 1000 g/mol and most preferably less than 750 g/mol; in a particular embodiment, the molar mass is between 100 and 750 g/mol or between 100 and 500 g/mol.

Preferred ionic liquids IL comprise at least one organic compound as a cation; most preferably, they comprise exclusively organic compounds as cations. Suitable organic cations are especially organic compounds having heteroatoms, such as nitrogen, sulfur or phosphorus; particular preference is given to organic compounds having a cationic group selected from an ammonium group, a sulfonium group and a phosphonium group. The ionic liquid IL may especially comprise salts of the general formula [A]_n ⁺[X]^n" where n is 1 , 2, 3 or 4, [A]⁺ is an ammonium cation, a sulfonium cation or a phosphonium cation, and [X]^n_ is a mono-, di-, tri- or tetravalent anion.

The ionic liquid IL may also comprise mixed salts comprising at least two different organic cations [A]⁺ or mixed salts comprising at least one organic cation [A]⁺ and one or two different mono-, di-, tri- or tetravalent metal cations [M]ⁿ⁺.

In a preferred embodiment, the at least one ionic liquid IL is at least one salt having a cation selected from imidazolium cations, pyridinium cations, pyrazolium cations and alkylammonium cations.

In a preferred embodiment, the ionic liquid IL is a combination of at least one first ionic liquid IL1 and at least one second ionic liquid IL2, the first ionic liquid IL1 comprising, as cation, at least one alkylammonium cation and the second ionic liquid IL2 comprising, as cation, at least one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom. Preferably, the composition comprises the at least two different ionic liquids IL1 and IL2 in a mass ratio of IL1 to IL2 in the range from 1 to 20, preferably 1 .5 to 10, more preferably from 2 to 6, especially preferably from 3 to 5, for example 4. Preferably, the composition comprises the at least two different ionic liquids IL1 and IL2 in a mass ratio of IL1 to IL2 in the range from 1 to 20, preferably 3 to 18, more preferably from 5 to 20, especially preferably from 7 to 15, for example 7.5 or 15.

Preferably, the ionic liquid IL, especially the ionic liquid IL1 , comprises, as cation, at least one, preferably exactly one, alkylammonium cation. In the context of the present invention, alkylammonium cation is understood to mean ammonium compounds having at least one C1-20- alkyl radical, preferably a Ci-18-alkyl radical, and a localized positive charge on the nitrogen atom. The compounds may be those having tetravalent nitrogen (quaternary ammonium compounds) or else be compounds having trivalent nitrogen, where one bond is a double bond. Preferably, the alkylammonium cation of the ionic liquid IL1 is a nonaromatic compound.

Useful ring systems include monocyclic, bicyclic, nonaromatic ring systems. Examples include bicyclic systems as described in WO 2008/043837. The bicyclic systems of WO 2008/043837 are diazabicyclo derivatives, preferably composed of one 7-membered and one 6-membered ring comprising an amidinium group; a particular example is the 1 ,8-diazabicyclo(5.4.0)undec-7- enium cation.

Preferably, the ionic liquid IL, especially the ionic liquid IL1 , comprises, as the sole cation, exactly one alkylammonium cation. The ionic liquid IL may alternatively be a mixed salt comprising at least one alkylammonium cation and at least one further organic cation [A]⁺ and/or at least one further metal cation [M]ⁿ⁺. Particularly preferred organic cations are quaternary ammonium cations having preferably four Ci-12-alkyl groups as substituents on the nitrogen atom. Preference is given to an ionic liquid IL comprising, as cation, at least one, preferably exactly one, alkylammonium cation of the general formula (I)

FT

I ₊

N-

I

R

n

(I)

is an organic group comprising 1 to 20, preferably 1 to 18, more preferably 1 to 12 and especially preferably 1 to 6 carbon atoms, where the organic group is a saturated or unsaturated, acyclic or cyclic aliphatic radical which may be unsubstituted or may be interrupted or substituted by 1 to 5 heteroatoms or functional groups;

R¹, R² and R³ are each independently: hydrogen; halogen, especially fluorine, chlorine, bromine and iodine, preferably chlorine; a Ci-Ci8-alkyl radical which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, Ci-C6-alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo and/or may be interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups; a C2-Ci8-alkenyl radical which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, C1-C6- alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo and/or may be interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups; a C5-Ci2-cycloalkyl radical which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, C1-C6- alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo; a C5-Ci2-cycloalkenyl radical which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, C1-C6- alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo; or a five- to six-membered heterocycle which includes oxygen, nitrogen and/or sulfur atoms and may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, Ci-C6-alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo, or two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) are an unsaturated or saturated five- to seven-membered ring which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, Ci-C6-alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo and may optionally be interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups;

X is an anion; and n is 1 , 2 or 3.

Possible heteroatoms in the definition of the R and R¹ to R³ radicals are in principle any heteroatoms capable in a formal sense of replacing a -CH2-, a -CH=, a -C≡ or a =C= group. If the carbon-comprising radical comprises heteroatoms, preference is given to oxygen, nitrogen, sulfur, phosphorus and silicon. Preferred groups especially include -0-, -S-, -SO-, -SO2-, -NR'-, - N=, -PR'-, -POR'- and -SiRV, where the R' radicals are the remaining portion of the radical comprising carbon atoms. In cases in which the R¹ to R³ radicals in the abovementioned formulae (I) are bonded to a carbon atom and not to a heteroatom, they can also be bonded directly via the heteroatom.

Possible functional groups are in principle all functional groups which can be bonded to a carbon atom or a heteroatom. Suitable examples include -OH (hydroxyl), =0 (especially in the form of a carbonyl group), -NH2 (amino), =NH (imino), -COOH (carboxyl), -CONH2

(carboxamide), -SO3H (sulfo) and -CN (cyano). Functional groups and heteroatoms may also be directly adjacent, and so combinations of a plurality of adjacent atoms, for instance -O- (ether), - S- (thioether), -COO- (ester), -CONH- (secondary amide) or -CONR'- (tertiary amide), are encompassed as well, for example di(Ci-C4-alkyl)amino, Ci-C4-alkyloxycarbonyl or C1-C4- alkyloxy.

Halogens are fluorine, chlorine, bromine and iodine. Preferably, the R radical is an unbranched or branched Ci-C2o-alkyl radical which is unsubstituted or mono- to

polysubstituted by hydroxyl, halogen, cyano, Ci-C6-alkoxycarbonyl and/or sulfo and preferably has a total of 1 to 20 carbon atoms, for example methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2- butyl, 2-methyl-1 -propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1 -pentyl, 2-pentyl, 3-pentyl, 2- methyl-1 -butyl, 3-methyl-1 -butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1 -propyl, 1 - hexyl, 2-hexyl, 3-hexyl, 2-methyl-1 -pentyl, 3-methyl-1 -pentyl, 4-methyl-1 -pentyl, 2-methyl-2- pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl- 1 -butyl, 2,3-dimethyl-1 -butyl, 3,3-dimethyl-1 -butyl, 2-ethyl-1 -butyl, 2,3-dimethyl-2-butyl, 3,3- dimethyl-2-butyl, 1 -heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 -undecyl, 1 -dodecyl, 1 -tetradecyl, 1 - hexadecyl, 1 -octadecyl, 2-hydroxyethyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl, 2- (ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, 6-hydroxyhexyl and propylsulfo; glycols, butylene glycols and oligomers thereof having 1 to 100, preferably 1 to 6 and especially preferably 1 to 3 units and a hydrogen or a Ci-C6-alkyl as end group, for example R^A0-(CHR^B- CH₂-0)p-CHR^B-CH₂- or R^A0-(CH2CH2CH2CH20)p-CH2CH2CH2CH₂0- where R^A and R^B are preferably hydrogen, methyl or ethyl and p is preferably 0 to 3, especially 3-oxabutyl, 3- oxapentyl, 3,6-dioxaheptyl, 3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxaundecyl, 3,6,9,12- tetraoxatridecyl and 3,6,9,12-tetraoxatetradecyl; vinyl; or an unsubstituted C5-Ci2-cycloalkenyl radical.

More preferably, the R radical is unbranched and unsubstituted Ci-Cis-alkyl, preferably C1-C1 alkyl, for example methyl, ethyl, 1 -propyl, 1 -butyl, 1 -pentyl, 1 -hexyl, 1 -heptyl, 1 -octyl, or is CH₃0-(CH2CH20)p-CH₂CH2- and CH₃CH20-(CH2CH20)p-CH₂CH2- with p = 0 to 3.

Preferably, the R¹, R² and R³ radicals are each independently hydrogen; a Ci-Cis-alkyl radical which may optionally be mono- to polysubstituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, Ci-C6-alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo, for example methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2- butyl, 2-methyl-1 -propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1 -pentyl, 2-pentyl, 3- pentyl, 2-methyl-1 -butyl, 3-methyl-1 -butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-

1 - propyl, 1 -hexyl, 2-hexyl, 3-hexyl, 2-methyl-1 -pentyl, 3-methyl-1 -pentyl, 4-methyl-1 - pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3- methyl-3-pentyl, 2,2-dimethyl-1 -butyl, 2,3-dimethyl-1 -butyl, 3,3-dimethyl-1 -butyl, 2-ethyl-1 - butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, 1 -heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, 1 -tetradecyl, 1 -hexadecyl, 1 -octadecyl, 2-hydroxyethyl, 2-cyanoethyl,

2- cyanopropyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n- butoxycarbonyl)ethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl, 3-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl, 6- methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-hydroxy-2,2-dimethylethyl, 2- methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2- ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl, 6-ethoxyhexyl, chloromethyl, 2-chloroethyl, trichloromethyl, 1 ,1 -dimethyl-2-chloroethyl, methoxymethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, 2- methoxyisopropyl and propylsulfo; a C5-Ci2-cycloalkyl radical which may optionally be substituted by Ci-C6-alkyl; for example cyclopentyl and cyclohexyl; glycols, butylene glycols and oligomers thereof having 1 to 100, preferably 1 to 6 and especially preferably 1 to 3 units and a hydrogen or a Ci-C6-alkyl as end group, for example R^A0-(CHR^B-CH₂-0)_P-CHR^B-CH₂- or

R^A0-(CH2CH2CH2CH20)p-CH2CH2CH2CH₂0- where R^A and R^B are preferably hydrogen, methyl or ethyl and p is preferably 0 to 3, especially 3-oxabutyl, 3-oxapentyl, 3,6- dioxaheptyl, 3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxaundecyl, 3,6,9,12- tetraoxatridecyl, 3,6,9,12-tetraoxatetradecyl, 5-hydroxy-3-oxapentyl, 8-hydroxy-3,6- dioxaoctyl, 1 1 -hydroxy-3,6,9-trioxaundecyl, 7-hydroxy-4-oxaheptyl, 1 1 -hydroxy-4,8- dioxaundecyl, 15-hydroxy-4,8,12-trioxapentadecyl, 9-hydroxy-5-oxanonyl, 14-hydroxy- 5,10-dioxatetradecyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 1 1 -methoxy- 3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 1 1 -methoxy-4,8-dioxaundecyl, 15-methoxy- 4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-dioxatetradecyl, 5- ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 1 1 -ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4- oxaheptyl, 1 1 -ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5- oxanonyl or 14-ethoxy-5,10-oxatetradecyl; or two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) are a saturated unsubstituted five- to seven-membered ring; for example, two adjacent R¹, R² and R³ radicals are 1 ,4-butylene, 1 ,5-pentylene or 3-oxa-1 ,5-pentylene.

In one embodiment, two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) may be an unsaturated or saturated five- to seven-membered ring which may optionally be substituted by functional groups selected from Ci-C6-alkyl, Ci-C6-alkyloxy, C1-C6- alkoxycarbonyl, hydroxyl, halogen, amino, cyano and sulfo and may optionally be interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups. Preferably, two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) form a saturated five- to seven-membered ring and two adjacent R¹, R² and R³ radicals are 1 ,4-butylene, 1 ,5-pentylene or 3-oxa-1 ,5-pentylene. Most preferably, the R¹, R² and R³ radicals are each independently hydrogen, unsubstituted Ci- Cis-alkyl, preferably Ci-Ci2-alkyl (for example methyl, ethyl, 1 -butyl, 1 -pentyl, 1 -hexyl, 1 -heptyl, 1 -octyl), 2-hydroxyethyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n- butoxycarbonyl)ethyl, chlorine, CH₃0-(CH2CH20)p-CH₂CH2- or CH₃CH20-(CH2CH20)p-CH₂CH2- where p = 0 to 3 or two adjacent R¹, R² and R³ radicals are 1 ,4-butylene, 1 ,5-pentylene or 3- oxa-1 ,5-pentylene.

More preferably, R¹, R² and R³ are a hydrogen atom or an above-described hydrocarbyl group having no further heteroatoms. Most preferably, R¹, R² and R³ are a hydrogen atom or an unsubstituted C1-C18 alkyl group, more preferably a C1-C6 alkyl group, for example a methyl group, ethyl group, propyl group, isopropyl group or n-butyl group.

More preferably, the at least one ionic liquid IL1 comprises an alkylammonium cation of formula (I)

I ₊

N -

I

R

(I)

where

R is an unbranched and unsubstituted Ci-Cis-alkyl (for example methyl, ethyl, 1 - propyl, 1 -butyl, 1 -pentyl, 1 -hexyl, 1 -heptyl, 1 -octyl, 1 -decyl, 1 -dodecyl, 1 -tetradecyl, 1 -hexadecyl, 1 -octadecyl, especially methyl, ethyl, 1 -butyl and 1 -octyl), CH3O- (CH₂CH20)p-CH₂CH2- or CH₃CH20-(CH2CH20)p-CH₂CH2- with p = 0 to 3;

R¹, R² and R³ are each independently: a hydrogen atom, unsubstituted Ci-Cis-alkyl (for example methyl, ethyl, 1 -butyl, 1 - pentyl, 1 -hexyl, 1 -heptyl, 1 -octyl), 2-hydroxyethyl, 2-cyanoethyl, 2- (methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, chlorine, CH₃0-(CH2CH20)p-CH₂CH2- or CH₃CH20-(CH2CH20)p-CH₂CH2- with p = 0 to 3, or two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) are a saturated unsubstituted five- to seven-membered ring, for example 1 ,4- butylene, 1 ,5-pentylene or 3-oxa-1 ,5-pentylene.

X is an anion; and is 1 , 2 or 3. More preferably, the ionic liquid IL1 comprises an alkylammonium cation of formula (I) where

R is Ci-Cis-alkyl, preferably Ci-C6-alkyl, and R¹, R² and R³ are each independently a hydrogen atom or Ci-Cis-alkyl, preferably Ci-C6-alkyl; or

R is Ci-Cis-alkyl, preferably Ci-C6-alkyl; R¹ and R² together are 1 ,5-pentylene or 3-oxa- 1 ,5-pentylene and R³ is a hydrogen atom or Ci-Cis-alkyl, preferably Ci-C6-alkyl.

Most preferred alkylammonium cations in the ionic liquid IL1 are methyltri(1 -butyl)ammonium, 1 - butyl-1 -methylpyrrolidinium, Ν,Ν-dimethylpiperidinium and N,N-dimethylmorpholinium.

Preferred anions, especially preferred X^n_ anions according to formula (I), are described below.

Especially preferred are ionic liquids IL comprising, as cation, methyltri(1 -butyl)ammonium and, as anion, an anion selected from chloride, bromide, hydrogensulfate, tetrachloroaluminate, thiocyanate, methylsulfate, ethylsulfate, methanesulfonate, formate, acetate,

dimethylphosphate, diethylphosphate, p-tolylsulfonate, tetrafluoroborate and

hexafluorophosphate.

Especially preferably, the ionic liquids IL1 are methyltri(1 -butyl)ammonium methylsulfate (MTBS) or 1 -butyl-1 -methylpyrrolidinium dimethylphosphate, more preferably methyltri(1 - butyl)ammonium methylsulfate (MTBS).

The alkylammonium cation of the ionic liquid IL may also be a heterocyclic ring system comprising at least one and preferably one or two tetra- and/or trivalent nitrogen(s), where one bond is a double bond. For example, the cation of the ionic liquid IL, especially of the ionic liquid IL1 , may be a cyclic nonaromatic alkylammonium cation selected from the group consisting of piperidinium cations, pyrazolium cations, pyrazolinium cations, imidazolinium cations, pyrrolidinium cations, imidazolidinium cations, guanidiumium cations and cholinium cations.

Suitable cations of the at least one ionic liquid IL, especially of the ionic liquid IL1 , are, for example, the cations of the general formulae (I I a) to (llj)

(H ') (Hi) (llj) where R is as defined above and the R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹ and R¹² radicals are each as defined above for the R¹, R² and R³ radicals.

In a preferred embodiment, the composition C may comprise an ionic liquid IL comprising, as cation, at least one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom, preferably one, two or three nitrogen atoms (also referred to as ionic liquid IL2). More particularly, the at least one nitrogen atom, preferably one, two or three nitrogen atoms, is in the ring system of the heterocycle. Preferably, the ionic liquid IL2 comprises, as cation, exactly one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom. The ionic liquid IL2 may alternatively be a mixed salt comprising at least one aromatic heterocycle and at least one further organic cation [A]⁺ and/or at least one further metal cation [M]ⁿ⁺.

The composition C may comprise the ionic liquid IL2 as the sole ionic liquid or in combination with other ionic liquids, especially in combination with the above-described ionic liquid comprising, as cation, at least one alkylammonium cation (ionic liquid IL1 ).

Most preferably, the ionic liquid IL comprises, as cation, a five- or six-membered heterocyclic aromatic ring system having one, two or three, preferably one or two, nitrogen atoms as part of the ring system. In principle, the five- or six-membered heterocyclic aromatic ring system may comprise one or two further heteroatoms, especially oxygen and/or sulfur atoms. The carbon atoms of the aromatic ring system may be substituted by organic groups having generally not more than 20 carbon atoms, preferably by a hydrocarbyl group, especially a C1-C16 alkyl group, especially a C1-C10 and more preferably a C1-C4 alkyl group.

Suitable cations of the at least one ionic liquid IL are, for example, the cations of the general formulae (Ilk) to (lis')

(Ms) (Ms') (Ms") where R is as defined above and the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are each as defined above for the R¹, R² and R³ radicals. Preferably, the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are each independently selected from hydrogen, methyl, ethyl, 1 -propyl, 1 -butyl and chlorine.

Preferably, the cation of the at least one ionic liquid IL2 is a cation of the abovementioned formulae (Ilk), (llo), (lip), (llq), (llq') and (Mr), most preferably a cation of the formula (llo).

Very particular preference is given to ionic liquids IL in which the cation is a pyridinium cation of the formula (Ilk) where one of the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals is methyl, ethyl or chlorine and the remaining R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen; or R⁶ is dimethylamino and the remaining R⁴, R⁵, R⁷ and R⁸ radicals are hydrogen; or all the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen; or

R⁵ is carboxyl or carboxamide and the remaining R⁴, R⁶, R⁷ and R⁸ radicals are hydrogen; or

R⁴ and R⁵ or R⁵ and R⁶ are 1 ,4-buta-1 ,3-dienylene and the remaining R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen. Especially preferred are ionic liquids IL in which the cation is a pyridinium cation of the formula (Ilk) where all the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen; or one of the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals is methyl or ethyl and the remaining R⁴, R⁵, R⁶,

R⁷ and R⁸ radicals are hydrogen.

Very particularly preferred pyridinium cations (Ilk) include 1 -methylpyridinium, 1 -ethylpyridinium, 1 -(1 -butyl)pyridinium, 1 -(1 -octyl)pyridinium, 1 -(1 -hexyl)pyridinium, 1 -(1 -octyl)pyridinium, 1 -(1 - dodecyl)pyridinium, 1 -(1 -tetradecyl)pyridinium, 1 -(1 -hexadecyl)pyridinium, 1 ,2- dimethylpyridinium, 1 -ethyl-2-methylpyridinium, 1 -(1 -butyl)-2-methylpyridinium, 1 -(1 -hexyl)-2- methylpyridinium, 1 -(1 -octyl)-2-methylpyridinium, 1 -(1 -dodecyl)-2-methylpyridinium, 1 -(1 - tetradecyl)-2-methylpyridinium, 1 -(1 -hexadecyl)-2-methylpyridinium, 1 -methyl-2-ethylpyridinium, 1 ,2-diethylpyridinium, 1 -(1 -butyl)-2-ethylpyridinium, 1 -(1 -hexyl)-2-ethylpyridinium, 1 -(1 -octyl)-2- ethylpyridinium, 1 -(1 -dodecyl)-2-ethylpyridinium, 1-(1 -tetradecyl)-2-ethylpyridinium, 1 -(1 - hexadecyl)-2-ethylpyridinium, 1 ,2-dimethyl-5-ethylpyridinium, 1 ,5-diethyl-2-methylpyridinium, 1 - (1 -butyl)-2-methyl-3-ethylpyridinium, 1 -(1 -hexyl)-2-methyl-3-ethylpyridinium and 1 -(1 -octyl)-2- methyl-3-ethylpyridinium, 1 -(1 -dodecyl)-2-methyl-3-ethylpyridinium, 1 -(1 -tetradecyl)-2-methyl-3- ethylpyridinium and 1 -(1 -hexadecyl)-2-methyl-3-ethylpyridinium.

Especially preferred are ionic liquids IL in which the cation is a pyridazinium cation of the formula (III) where all the R⁴, R⁵, R⁶ and R⁷ radicals are hydrogen; or one of the R⁴, R⁵, R⁶ and R⁷ radicals is methyl or ethyl and the remaining R⁴, R⁵, R⁶ and R⁷ radicals are hydrogen. Especially preferred are ionic liquids IL in which the cation is a pyrimidinium cation of the formula (Mm) where

R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each independently hydrogen or methyl; or

R⁴ is hydrogen, methyl or ethyl, R⁵ and R⁶ are methyl and R⁷ is hydrogen.

Especially preferred are ionic liquids IL in which the cation is a pyrazinium cation of the formula (I In) where

R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each independently hydrogen or methyl; or R⁴ is hydrogen, methyl or ethyl, R⁵ and R⁶ are methyl and R⁷ is hydrogen; or

R⁴, R⁵, R⁶ and R⁷ are methyl, or R⁴, R⁵, R⁶ and R⁷ are hydrogen.

Especially preferred are ionic liquids IL in which the cation is an imidazolium cation of the formula (No) where

R⁴ is hydrogen, methyl, ethyl, 1 -propyl, 1 -butyl, 1 -pentyl, 1 -hexyl, 1 -octyl, 2-hydroxyethyl or 2-cyanoethyl and R⁵, R⁶ and R⁷ are each independently hydrogen, methyl or ethyl.

Very particularly preferred imidazolium cations (No) include 1 -methylimidazolium, 1 - ethylimidazolium, 1 -(1 -butyl)imidazolium, 1 -(1 -octyl)imidazolium, 1 -(1 -dodecyl)imidazolium, 1 -(1 - tetradecyl)imidazolium, 1 -(1 -hexadecyl)imidazolium, 1 ,3-dimethylimidazolium, 1 -ethyl-3- methylimidazolium, 1 -(1 -butyl)-3-methylimidazolium, 1 -(1 -butyl)-3-ethylimidazolium, 1 -(1 -hexyl)- 3-methylimidazolium, 1 -(1 -hexyl)-3-ethylimidazolium, 1 -(1 -hexyl)-3-butylimidazolium, 1 -(1 -octyl)- 3-methylimidazolium, 1 -(1 -octyl)-3-ethylimidazolium, 1 -(1 -octyl)-3-butylimidazolium, 1 -(1 - dodecyl)-3-methylimidazolium, 1 -(1 -dodecyl)-3-ethylimidazolium, 1 -(1 -dodecyl)-3- octylimidazolium, 1 -(1 -tetradecyl)-3-methylimidazolium, 1 -(1 -tetradecyl)-3-ethylimidazolium, 1 - (1 -tetradecyl)-3-butylimidazolium, 1 -(1 -tetradecyl)-3-octylimidazolium, 1 -(1 -hexadecyl)-3- methylimidazolium, 1 -(1 -hexadecyl)-3-ethylimidazolium, 1 -(1 -hexadecyl)-3-butylimidazolium, 1 - (1 -hexadecyl)-3-octylimidazolium, 1 ,2-dimethylimidazolium, 1 ,2,3-trimethylimidazolium, 1 -ethyl- 2,3-dimethylimidazolium, 1 -(1 -butyl)-2,3-dimethylimidazolium, 1 -(1 -hexyl)-2,3- dimethylimidazolium, 1 ,4-dimethylimidazolium, 1 ,3,4-trimethylimidazolium, 1 ,4-dimethyl-3- ethylimidazolium, 3-butylimidazolium, 1 ,4-dimethyl-3-octylimidazolium, 1 ,4,5- trimethylimidazolium, 1 ,3,4,5-tetramethylimidazolium, 1 ,4,5-trimethyl-3-ethylimidazolium, 1 ,4,5- trimethyl-3-butylimidazolium and 1 ,4,5-trimethyl-3-octylimidazolium. Especially preferred are ionic liquids IL in which the cation is a pyrazolium cation of the formula (lip) where

R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each independently hydrogen or methyl.

Especially preferred are ionic liquids IL in which the cation is a thiazolium cation of the formula (llq) or (llq') or an oxazolium cation of the formula (Mr) where R⁴ is hydrogen, methyl, ethyl or phenyl and R⁵, R⁶ and R⁷ are each independently hydrogen or methyl.

Especially preferred are ionic liquids IL in which the cation is a 1 ,2,4-triazolium cation of the formula (lis), (lis') or (lis") where

R⁴ and R⁵ are each independently hydrogen, methyl, ethyl or phenyl and R⁶ is hydrogen, methyl or phenyl.

In a preferred embodiment, the ionic liquid IL, especially the at least one ionic liquid IL2, comprises, as cation, at least one, preferably exactly one, cation selected from the group consisting of pyridinium cations, pyridazinium cations, pyrimidinium cations, pyrazinium cations, imidazolium cations, pyrazolium cations, thiazolium cations and triazolium cations.

These cations are listed, for example, in WO 2005/1 13702. If necessary for a positive charge on the nitrogen atom or in the aromatic ring system, the nitrogen atoms are each substituted by an organic group having generally not more than 20 carbon atoms, preferably a hydrocarbyl group, especially a C1-C16 alkyl group, especially a C1-C10 alkyl group and more preferably a C1-C4 alkyl group. Particularly preferred cations of IL are imidazolium cations, pyrimidinium cations and pyrazolium cations, which are understood to mean compounds having an imidazolium, pyrimidinium or pyrazolium ring system and optionally any desired substituents on the carbon and/or nitrogen atoms of the ring system. Particularly preferred cations of IL2 are imidazolium cations, pyridinium cations and pyrazolium cations, which are understood to mean compounds having an imidazolium, pyridinium or pyrazolium ring system and optionally any desired substituents on the carbon and/or nitrogen atoms of the ring system. Preferably, the ionic liquid IL, especially the at least one ionic liquid IL2, comprises at least one, preferably exactly one, imidazolium cation as cation. More preferably, the ionic liquid IL comprises, as the sole cation, at least one, preferably exactly one, imidazolium cation. In a particularly preferred embodiment, the ionic liquid IL is a compound of the formula comprising an imidazolium cation

n

(III) in which

R, R⁴, R⁵, R⁶ and R⁷ are each as defined above; X is an anion, and n is 1 , 2 or 3.

Preferably, the R⁴, R⁵, R⁶ and R⁷ and R⁸ radicals are each independently selected from hydrogen, Ci-Ci2-alkyl, preferably Ci-C6-alkyl, and halogen, especially selected from hydrogen, methyl, ethyl, 1 -propyl, 1 -butyl and chlorine.

The variable n is preferably 1. Usable anions, especially as anion X"-, according to the formulae (I) and (III), are in principle any anions which, in conjunction with the cation, lead to an ionic liquid.

The anion, especially the anion X"-, may be an organic or inorganic anion. Particularly preferred ionic liquids consist exclusively of the salt of an organic cation with one of the anions specified below.

The anion, especially the anion X^n_ according to the formulae (I) and (III) of the ionic liquid IL, is, for example, selected from: the group of the halides and halogen compounds of the formulae:

P; CI-; Br; |-; BF₄-; PF₆-; AlCk; AI2CI7-, AlsCho^", AIBr₄-; CF3SO3-, (CF₃S0₃)₂N-, CF₃C0₂-, CCI3CO2-, CN-, SCN-, OCN-, NO2-, NO3-; the group of the sulfates, sulfites and sulfonates of the formulae:

S0₄2-, HS0₄-, SO3²-, HSO3-, R^aOS0₃-, R^aS0₃-; the group of the phosphates of the formulae: PO4³-, HPO4²-, H2PO4-, R^aP0₄ ²-, HR^aP0₄-, R^aR^bP0₄-: the group of the phosphonates and phosphinates of the formulae:

R^aHP0₃-, R^aR^bP0₂ ^", R^aR^bP0₃-; the group of the carboxylates of the general formula:

R^aCOO-; the group of the borates of the general formulae:

BO3³-, HBO3²-, H2BO3-, R^aR^bB0₃ ^", RaHBOs^", RaBOs^2", B(OR^a)(OR )(OR^c)(OR^d)-, B(HS0₄)-

, B(R^aS0₄)- ; the group of the boronates of the general formulae:

R^aB0₂ ²-, R^aR^bBO-; the group of the carbonates and carbonic esters of the general formulae:

the group of the carboximides, bis(sulfonyl)imides and sulfonylimides of the

formulae:

the group of the alkoxides and aryl oxides of the general formula:

R^aO-; where R^a, R^b, R^c and R^d in the aforementioned anions are each independently selected from: hydrogen or Ci-Ci2-alkyl and the cycloalkyl-, halogen-, hydroxyl-, amino-, carboxyl-, formyl-, -0-, -CO-, -CO-O- or -CO-N<-substituted components thereof, for example methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, 2-methyl-1 -propyl (isobutyl), 2-methyl-2- propyl (tert-butyl), 1 -pentyl, 2-pentyl, 3-pentyl, 2-methyl-1 -butyl, 3-methyl-1 -butyl, 2- methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1 -propyl, 1 -hexyl, 2-hexyl, 3-hexyl, 2- methyl-1 -pentyl, 3-methyl-1 -pentyl, 4-methyl-1 -pentyl, 2-methyl-2-pentyl, 3-methyl-2- pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1 -butyl, 2,3- dimethyl-1 -butyl, 3,3-dimethyl-1 -butyl, 2-ethyl-1 -butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2- butyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy, ethoxy, formyl, acetyl or CF3. More preferably, R^a, R^b, R^c and R^d in the aforementioned anions are each independently a hydrogen atom or an unsubstituted Ci-Ci2-alkyl group, preferably Ci-C6-alkyl group.

Particularly preferred anions, especially very particularly preferred anions X^n", are: chloride, bromide, hydrogensulfate, tetrachloroaluminate, thiocyanate, methylcarbonate, methylsulfate, ethylsulfate, methanesulfonate, formate, acetate, dimethylphosphate,

diethylphosphate, p-tolylsulfonate, tetrafluoroborate, hexafluorophosphate,

bis(trifluoromethylsulfonyl)imide and bis(methylsulfonyl)imide.

Very particularly preferred anions, especially very particularly preferred anions X^n", are: chloride, hydrogensulfate, methylsulfate, ethylsulfate, methanesulfonate, formate and acetate. Especially preferred are ionic liquids IL comprising, as cation, at least one cation, preferably exactly one cation, selected from the group consisting of

1 -methylimidazolium, 1 -ethylimidazolium, 1 -(1 -butyl)imidazolium, 1 -(1 -octyl)imidazolium, 1 -(1 -dodecyl)imidazolium, 1 -(1 -tetradecyl)imidazolium, 1 -(1 -hexadecyl)imidazolium, 1 ,3- dimethylimidazolium, 1 -ethyl-3-methylimidazolium, 1 -(1 -butyl)-3-methylimidazolium, 1 -(1 - butyl)-3-ethylimidazolium, 1 -(1 -hexyl)-3-methylimidazolium, 1 -(1 -hexyl)-3- ethylimidazolium, 1 -(1 -hexyl)-3-butylimidazolium, 1 -(1 -octyl)-3-methylimidazolium, 1 -(1 - octyl)-3-ethylimidazolium, 1 -(1 -octyl)-3-butylimidazolium, 1 -(1 -dodecyl)-3- methylimidazolium, 1 -(1 -dodecyl)-3-ethylimidazolium, 1 -(1 -dodecyl)-3-butylimidazolium, 1 -(1 -dodecyl)-3-octylimidazolium, 1 -(1 -tetradecyl-3-methylimidazolium, 1 -(1 -tetradecyl)- 3-ethylimidazolium, 1 -(1 -tetradecyl)-3-butylimidazolium, 1 -(1 -tetradecyl-3- octylimidazolium, 1 -(1 -hexadecyl)-3-methylimidazolium, 1 -(1 -hexadecyl)-3- ethylimidazolium, 1 -(1 -hexadecyl)-3-butylimidazolium, 1 -(1 -hexadecyl-3- octylimidazolium, 1 ,2-dimethylimidazolium, 1 ,2,3-trimethylimidazolium, 1 -ethyl-2,3- dimethylimidazolium, 1 -(1 -butyl)-2,3-dimethylimidazolium, 1 -(1 -hexyl)-2,3- dimethylimidazolium, 1 -(1 -octyl)-2,3-dimethylimidazolium, 1 ,4-dimethylimidazolium,

1 .3.4- trimethylimidazolium, 1 ,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1 ,4- dimethyl-3-octylimidazolium, 1 ,4,5-trimethylimidazolium, 1 ,3,4,5-tetramethylimidazolium,

1 .4.5- trimethyl-3-ethylimidazolium, 1 ,4,5-trimethyl-3-butylimidazolium, 1 ,4,5-trimethyl-3- octylimidazolium; and 1 -butyl-1 -methylpyrrolidinium; and, as anion, at least one anion, preferably exactly one anion, selected from the group consisting of chloride, bromide, hydrogensulfate, tetrachloroaluminate, thiocyanate, methylsulfate, ethylsulfate, methanesulfonate, formate, acetate, dimethylphosphate, diethylphosphate, p-tolylsulfonate, tetrafluoroborate and hexafluorophosphate. Particular preference is additionally given to ionic liquids IL selected from the group consisting of:

1 ,3-dimethylimidazolium methylsulfate, 1 ,3-dimethylimidazolium hydrogensulfate, 1 ,3- dimethylimidazolium dimethylphosphate, 1 ,3-dimethylimidazolium acetate, 1 -ethyl-3- methylimidazolium methylsulfate, 1 -ethyl-3-methylimidazolium ethylsulfate, 1 -ethyl-3- methylimidazolium hydrogensulfate, 1 -ethyl-3-methylimidazolium thiocyanate, 1 -ethyl-3- methylimidazolium acetate, 1 -ethyl-3-methylimidazolium methanesulfonate, 1 -ethyl-3- methylimidazolium diethylphosphate, 1 -(1 -butyl)-3-methylimidazolium methylsulfate, 1 -(1 - butyl)-3-methylimidazolium hydrogensulfate, 1 -(1 -butyl)-3-methylimidazolium thiocyanate,

1 -(1 -butyl)-3-methylimidazolium acetate, 1 -(1 -butyl)-3-methylimidazolium

methanesulfonate, methyltri(1 -butyl)ammonium methylsulfate, 1 -butyl-1 - methylpyrrolidinium dimethylphosphate, Ν,Ν-dimethylpiperidinium and N,N- dimethylmorpholinium.

In a particularly preferred embodiment, the composition C comprises at least one ionic liquid IL selected from the group consisting of 1 -ethyl-3-methylimidazolium methylsulfate, 1 -ethyl-3- methylimidazolium ethylsulfate, 1 -ethyl-3-methylimidazolium hydrogensulfate, 1 -ethyl-3- methylimidazolium acetate, 1 -ethyl-3-methylimidazolium methanesulfonate, methyltri(1 - butyl)ammonium methylsulfate (MTBS) and 1 -butyl-1 -methylpyrrolidinium dimethylphosphate.

In one embodiment, the composition C comprises as the first ionic liquid IL1 methyltri(1 -butyl)ammonium methylsulfate (MTBS); and as the second ionic liquid IL2 a compound selected from the group consisting of

1 ,3-dimethylimidazolium methylsulfate, 1 ,3-dimethylimidazolium hydrogensulfate, 1 ,3- dimethylimidazolium dimethylphosphate, 1 ,3-dimethylimidazolium acetate, 1 -ethyl-3- methylimidazolium methylsulfate, 1 -ethyl-3-methylimidazolium hydrogensulfate, 1 -ethyl-3- methylimidazolium thiocyanate, 1 -ethyl-3-methylimidazolium acetate, 1 -ethyl-3- methylimidazolium methanesulfonate, 1 -ethyl-3-methylimidazolium diethylphosphate, 1 - (1 -butyl)-3-methylimidazolium methylsulfate, 1 -(1 -butyl)-3-methylimidazolium

hydrogensulfate, 1 -(1 -butyl)-3-methylimidazolium thiocyanate, 1 -(1 -butyl)-3- methylimidazolium acetate, 1 -(1 -butyl)-3-methylimidazolium methanesulfonate, 1 -(1 - dodecyl)-3-methylimidazolium methylsulfate, 1 -(1 -dodecyl)-3-methylimidazolium hydrogensulfate, 1 -(1 -tetradecyl)-3-methylimidazolium methylsulfate, 1 -(1 -tetradecyl)-3- methylimidazolium hydrogensulfate, 1 -(1 -hexadecyl)-3-methylimidazolium methylsulfate and 1 -(1 -hexadecyl)-3-methylimidazolium hydrogensulfate, preferably selected from 1 -ethyl-3-methylimidazolium methylsulfate, 1 -ethyl-3- methylimidazolium hydrogensulfate, 1 -ethyl-3-methylimidazolium acetate and 1 -ethyl-3- methylimidazolium methanesulfonate. Further constituents of composition C The composition of the invention and the composition C used in the process of the invention may comprise further constituents in addition to the at least one ionic liquid IL.

Possible examples of these include additives with which a desired viscosity and/or a desired melting point is established. These include, for example, solvents, especially water and/or organic solvents miscible with the ionic liquid.

In a preferred embodiment, the composition C comprises:

0% to 100% by weight, preferably 60% to 90% by weight and more preferably 60% to 80% by weight, based on the overall composition C, of the at least one ionic liquid IL;

0% to 45% by weight, preferably 0% to 30% by weight, more preferably 1 % to 30% by weight and most preferably 5% to 20% by weight, based on the overall composition C, of at least one solvent S.

In a preferred embodiment, the composition C consists of the abovementioned components, i.e. the abovementioned components add up to 100% by weight.

Preferably, the composition C is a solution; more particularly, the components of composition C are homogeneously miscible with one another or the components of composition C are in homogeneously distributed form. More particularly, the composition C is a solution having molecular dispersion.

The composition C may especially comprise water or an organic solvent miscible with water and the ionic liquid IL or a mixture thereof as solvent S.

The viscosity of the composition C (etch composition) is preferably in the range from 20 to 200 mPas, preferably in the range from 30 to 100 mPas and more preferably in the range from 30 to 70 mPas (in each case by dynamic means at 60°C).

The melting point of the composition C is typically below 100°C, preferably below room temperature (25°C), especially preferably below 10°C, more preferably below 0°C.

Preferably, the composition C comprises at least one solvent S selected from water, propylene carbonate, polyethylene glycols, mono-, di- or triesters of glycol and C1-C6 carboxylic acids, especially diacetin (glyceryl diacetate) and triacetin (glyceryl triacetate), glycols, especially ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol. Preference is given to polyethylene glycols having a molecular weight in the range of 200-4000 g/mol, preferably 200-1000 g/mol, more preferably 200-600 g/mol.

More preferably, the composition C comprises 1 % to 30% by weight, preferably 5% to 20% by weight and more preferably 7% to 15% by weight, based on the overall composition C, of at least one solvent S selected from propylene carbonate, polyethylene glycol, especially PEG 200, triacetin and water.

In a preferred embodiment, the composition C comprises:

49% to 94% by weight, preferably 55% to 85% by weight and more preferably 60% to 80% by weight, based on the overall composition C, of at least one above-described ionic liquid IL comprising at least one alkylammonium cation; 5% to 50% by weight, preferably 5 to 40% by weight, preferably 10% to 40% by weight, also preferably 5 to 20 % by weight and more preferably 10% to 20% by weight, based on the overall composition C, of at least one above-described ionic liquid IL2 comprising, as cation, at least one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom;

1 % to 30% by weight, preferably 5% to 20% by weight, based on the overall composition C, of at least one solvent S selected from the group consisting of water, propylene carbonate, polyethylene glycols, mono-, di- or triesters of glycol and C1-C6 carboxylic acids, and glycols, preferably selected from the group consisting of water, propylene carbonate, polyethylene glycols, diacetin (glyceryl diacetate), triacetin (glyceryl triacetate), ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol.

In another preferred embodiment, the composition C comprises 49% to 94% by weight, preferably 55% to 85% by weight and more preferably 60% to

80% by weight, based on the overall composition C, of the at least one ionic liquid IL1 ;

5% to 50% by weight, preferably 5% to 30% by weight and more preferably 5% to 20% by weight, based on the overall composition C, of the at least one ionic liquid IL2;

1 % to 30% by weight, preferably 10% to 30% by weight, based on the overall composition C, of at least one solvent S as described above.

In a preferred embodiment, the composition C comprises exclusively propylene carbonate as solvent S. It is additionally possible that the composition comprises a mixture of propylene carbonate and water as solvent S, in which case the proportion of propylene carbonate, based on the overall solvent S, is at least 30% by weight, preferably at least 50% by weight, more preferably at least 90% by weight. The composition consists preferably to an extent of more than 10% by weight, especially to an extent of more than 30% by weight, more preferably to an extent of more than 50% by weight and most preferably to an extent of more than 80% by weight of the at least one ionic liquid IL. In a particularly preferred embodiment, it consists to an extent of more than 90% by weight and especially to an extent of more than 95% by weight of the at least one ionic liquid IL. In a further embodiment, the composition consists exclusively of one or more of the above-described ionic liquids, preferably of the ionic liquids IL1 and IL2. The ionic liquid and composition C which comprises or consists of the ionic liquid are preferably liquid over the entire temperature range from 20 to 100°C (at standard pressure, 1 bar).

The process

An essential element in the process of the invention is the pretreatment according to the claims of the plastics or the plastic surface. The various process steps for chemical and electrolytic coating with metal and further measures for performance, preparation and finishing that are necessary or advisable for the purpose are described in a wide variety of different embodiments in the prior art, for example in DE-A 100 54 544, Schlesinger et al. "Modern Electroplating" chapter 18, pages 450-457 (5th edition, 2010, John Wiley & Sons Inc., ISBN 978-0-470-16778- 6) or Kanani "Galvanotechnik" [Electroplating Technology] (Carl Hanser Verlag, 2000, ISBN 3- 446-21024-5). Even prior to the pretreatment of the invention in step a), cleaning and/or degreasing of the plastic surface to be coated may be advisable. Cleaning and degreasing of this kind can be conducted with standard cleaning compositions or detergents.

Step a)

The process of the invention comprises, in step a), the pretreatment of the plastic surface with a composition C (etch solution) comprising at least one ionic liquid IL. Preferred ionic liquids and optional further constituents of the composition C are described above. It has been found that, surprisingly, observing optimized treatment conditions, especially the temperature and duration of the pretreatment, gives particularly advantageous metal coatings.

Preferably, the pretreatment of the plastic surface with the composition C in step a) is effected at a temperature of 30 to 120°C, more preferably of 40 to 120°C, especially preferably of 50 to 65°C and most preferably 50 to 60°C. Preferably, the composition C has the above temperature for the purpose. There is often no need for preceding separate heating of the plastic surface to be coated, or of the plastic molding to be coated. Preferably, the pretreatment of the plastic surface with the composition C in step a) is effected over a period of 1 to 60 min, preferably 1 to 30 min, especially preferably 2 to 20 min and more preferably 5 to 10 min. Preferably, the pretreatment of the plastic surface with the composition C in step a) is effected at a temperature in the range from 50 to 65°C and over a period of 5 to 20 min. More preferably, the pretreatment of the plastic surface with the composition C in step a) is effected at a temperature in the range from 50 to 60°C and over a period of 5 to 15 min. In a preferred embodiment, the invention relates to a process for coating a plastic surface, especially a plastic molding, consisting of or comprising acrylonitrile/butadiene/styrene copolymer ABS, wherein the pretreatment of the plastic surface, especially of the plastic molding, with the composition C in step a) is effected at a temperature in the range from 50 to 60°C, preferably 50 to 55°C, and over a period of 5 to 15 min, preferably 5 to 10 min. The plastic surface consisting or comprising acrylonitrile/butadiene/styrene copolymer (ABS) may especially be a plastic molding consisting essentially of ABS, of a blend comprising ABS, e.g. ABS/PC (acrylonitrile/butadiene/styrene copolymer and polycarbonate), and/or a

multicomponent plastic comprising ABS. In a preferred embodiment, the plastic surface to be coated, especially the plastic molding to be coated, is dipped into the composition C, where the composition C preferably has the above temperature. In this case, the composition C can be agitated for better mass transfer, which can be effected by stirring, pumping, blowing air in, etc. Alternatively, the plastic surface itself can also be agitated in the composition C by means of specific devices known in electroplating. The person skilled in the art is aware of suitable methods for the purpose.

The required amount of composition C is adjusted in such a way that the plastic surface is wetted to the desired degree. The plastic surface or the plastic molding can be immersed completely or else partially.

The viscosity of the composition C (etch solution) is preferably in the range from 20 to 200 mPas, preferably in the range from 30 to 100 mPas and more preferably in the range from 30 to 70 mPas (dyn., 60°C).

Step b)

The process of the invention comprises, in step b), the treating of the plastic surface from step a) with an aqueous rinse solution RS while applying ultrasound. The treatment in step b) can especially remove the adhering composition C, but also partly dissolved plastic particles, from the surface, especially from the surface of the plastic molding. In a preferred embodiment, the treating of the plastic surface with the aqueous rinse solution RS with application of ultrasound in step b) is effected by dipping the plastic surface from step a) into an ultrasound bath comprising the aqueous rinse solution RS for a period of 1 to 30 min, preferably 2 to 20 min and more preferably 5 to 15 min. In particular an sufficient rinsing might be obtained after 1 to 2 min, in particular at about 90 sec. Preferably, step b) is effected by dipping the plastic surface from step a) into an ultrasound bath comprising the aqueous rinse solution RS for a period of 1 to 2 min at a temperature in the range from 40 to 60°C.

In a preferred embodiment, the treating of the plastic surface, especially the plastic molding, with the aqueous rinse solution RS while applying ultrasound in step b) is effected by dipping the plastic surface, especially the plastic molding, from a) into an ultrasound bath comprising the aqueous rinse solution RS at a power in the range from 40 to 60 watts/L, over a period of 1 to 30 min and at a temperature of 40 to 60°, and wherein the aqueous rinse solution RS comprises at least 85% by weight of water, preferably at least 95% by weight.

The aqueous rinse solution RS preferably comprises water or a mixture of water and one or more water-miscible organic solvents, where the proportion of water is generally at least 85% by weight, preferably at least 95% by weight and more preferably at least 98% by weight, based in each case on the overall rinse solution. Organic solvents used may be known polar water- miscible solvents such as alcohols or dimethyl sulfoxide (DMSO). Organic solvents used may especially be water-miscible alcohols such as methanol, ethanol or propanol. In a preferred embodiment, the rinse solution RS consists exclusively of water.

The rinse solution RS may optionally comprise the additions known to those skilled in the art, for example surfactants.

The pH of the rinse solution RS is preferably in the range from 5 to 8, especially from 6 to 7. Preferably, the rinse step b), which may also consist of a plurality of steps, is conducted at a temperature in the range from 10 to 80°C, preferably 20 to 70°C, more preferably at 40 to 60°C.

The ultrasound treatment is preferably effected at frequencies in the range from 20 to 400 kHz, preferably 30 to 50 kHz. The ultrasound treatment is preferably effected at a power in the range from 10 to 100 watts/L, preferably from 40 to 60 watts/L. Especially preferably, the ultrasound treatment is effected at a power in the range from 40 to 60 watts/L, over a period of 5 to 15 min and a temperature of 40 to 60°C. Further preferred, the ultrasound treatment is effected at a power in the range from 40 to 60 watts/L, over a period of 1 to 2 min and a temperature of 40 to 60°C.

Preferably, step b) may comprise a plurality of rinse steps, especially further rinse steps without application of ultrasound. Preferably, the treating of the plastic surface with an aqueous rinse solution RS in step b) may comprise, as an additional step, the treating of the plastic surface with at least one further aqueous rinse solution RS, especially water, which may be effected, for example, by spraying or dipping the plastic surface. A preferred embodiment relates to a process as described, wherein step b) comprises (and preferably consists of) the following steps: b1 ) treating the plastic surface, especially the plastic molding, from step a) with a first aqueous rinse solution RS1 , by spraying the plastic surface, especially the plastic molding, with the first aqueous rinse solution RS1 or dipping it into the first aqueous rinse solution RS1 ; b2) treating the plastic surface, especially the plastic molding, from step b1 ) with a

second aqueous rinse solution RS2 while applying ultrasound.

The process of the invention, especially steps a) and/or b), can be conducted partly or fully continuously or quasi-continuously.

In one embodiment, the composition C is recovered after step a) and fed fully or partly back to the etching step a) (recycling). The recycling of the composition C can be effected, for example, by a precipitation of the dissolved plastic by means of water or an organic solvent and subsequent removal of the dissolved plastic by a filtration. The medium/media utilized for precipitation can subsequently be recovered by distillation. It is also possible to remove volatile constituents of the dissolved plastic from the composition by direct distillation. In this way, it is possible to obtain a purified and reusable composition C.

In a preferred embodiment, the rinse solution RS is recovered after step b), especially after steps b1 ) and/or b2), and fed fully or partly back to the rinse steps b), especially the rinse steps b1 ) and/or b2) (recycling). Preferably, the spent rinse solution is cleaned beforehand, for example by filtration.

The recycling of the rinse solutions RS can be effected, for example, by removing the plastic present therein, preferably by a filtration. In this way, it is possible to obtain a cleaned and reusable rinse solution (which is generally a mixture of water and ionic liquid IL) which can then be recycled fully or partly to rinse steps b1 ) and/or b2). Preferably, a portion of the rinse solution recovered is discharged, especially in order to prevent enrichment of ionic liquid in the rinse solution RS in the circuit.

Step c)

The process of the invention comprises, in step c), the treating of the plastic surface from step b) with an activator composition A comprising at least one ionogenic and/or colloidal activator, especially at least one palladium component P, preferably at least one colloidal palladium component P. Typically, step c) comprises, especially in combination with step d), the applying of metal nuclei, preferably of metal nuclei of palladium, silver or gold, more preferably of palladium. Step b) is typically referred to as activation. Preferably, the manner of activation and the first metal coating in step e) are matched to one another.

Known methods for activation are, for example, conventional colloidal activation (application of palladium/tin colloids), ionogenic activation (application of palladium cations), direct

metallization or processes known by the Udique Plato®, Enplate MID select or LDS Process names.

For example, activation with ionogenic systems can be accomplished by first treating the plastic surface with tin(ll) ions, generally with formation of firmly adhering gels of tin oxide hydrate on rinsing with water after the treatment with the tin(ll) ions. In the subsequent treatment with a palladium salt solution, palladium nuclei are normally formed on the plastic surface through reduction with the tin(ll) species, and these typically serve as catalyst/metal nucleus for the later chemical metallization (step e)).

For activation with colloidal systems, it is possible to use noble metal colloid compositions, especially colloids of the gold group (transition group I) and platinum group of the Periodic Table. Preference is given to using colloidal solutions of palladium, silver or gold, especially preferably colloidal solutions of palladium. In the colloidal solution, the metal nuclei, for example the palladium nuclei, are typically surrounded by the protective colloid shell. It is possible with preference to use palladium colloid solutions which form through reaction of palladium chloride with tin(ll) chloride in the presence of excess hydrochloric acid.

The concentration of the at least one ionogenic and/or colloidal activator P in the activator composition A is typically 20 to 150 mg/L.

Typical palladium-containing activator systems and further details of the activation step are described in Annual Book of ASTM Standard, Vol. 02.05 "Metallic and Inorganic Coatings; Metal Powders, Sintered P/M Structural Parts", Standard Practice for Preparation of Plastic Materials for Electroplating, 1995, pages 446-450.

Typically, the activator P used may be a standard commercially available palladium activator, for example "Activator U" from HSO or "Surtec 961 Pd" from Surtec.

Step d)

The process of the invention comprises, in step d), the treating of the plastic surface from step c) with an accelerator composition B comprising an acid and/or a reducing agent. The treatment of the plastic surface with the accelerator composition B especially frees the metal nuclei adsorbed on the surface (especially in the depressions), especially palladium, silver or gold nuclei, of the protective colloid shell and/or reduces the absorbed metal salts to the metal. The treatment of the plastic surface with the accelerator composition B typically gives rise to metal nuclei on the plastic surface, preferably metal nuclei of palladium, silver or gold, more preferably of palladium. These metal nuclei typically serve as the starting point (catalyst) for the subsequent chemical metal deposition in step e).

According to the invention, the accelerator composition B comprises at least one reducing agent and/or an acid which is particularly suitable for removing the protective metal colloid shell and/or for reducing metal salts present at the surface to the metal. Preferably, the at least one reducing agent is selected from alkali metal, ammonium or alkaline earth metal fluoroborate, for example sodium tetrafluoroborate (NaBF₄), peroxides, sulfites, hydrogensulfites, hydrazine and salts thereof, hydroxylamine and salts thereof. Preferably, the at least one acid is selected from hydrochloric acid, methanesulfonic acid, citric acid, ascorbic acid, tartaric acid, tetrafluoroboric acid (HBF₄).

The pH of the accelerator composition B may especially be set within a range from 0 to 7, preferably from 1 to 2.

The concentration of the acid and/or the reducing agent in the accelerator composition B is typically 0.4 to 0.5 N; the concentration is especially 0.45 N (pH 1.5).

Typical accelerator compositions and further details of the acceleration step are described in Annual Book of ASTM Standard, Vol. 02.05 "Metallic and Inorganic Coatings; Metal Powders, Sintered P/M Structural Parts", Standard Practice for Preparation of Plastic Materials for Electroplating, 1995, pages 446-450.

Typically, the accelerator composition B used may be a standard commercially available accelerator, for example "HSO Accelerator" from HSO or "Surtec 961 A" from Surtec.

Step e)

A further constituent of the process of the invention is the application of what is called a first metal coating, which is typically effected by electroless means (chemical metal deposition). In general, the first layer applied by electroless means (seed layer) is a layer of nickel, copper, chromium or alloys thereof. Preference is given to one or more layers of nickel and/or copper. Particular preference is given to exactly one layer consisting essentially of nickel. The process of the invention comprises, in step e), the chemical deposition of a metal layer, preferably of a metal layer consisting essentially of nickel, by treating the plastic surface, especially the plastic molding, from step d) with a coating composition M1 comprising at least one metal salt, preferably at least one nickel(ll) salt, and at least one reducing agent, preferably an in situ reducing agent.

Further preferably, step e) comprises the chemical deposition of a metal layer consisting essentially of nickel and/or copper, by treating the surface from step d) with a coating composition M1 comprising at least one nickel(ll) salt and/or one copper(ll) salt, and at least one reducing agent, preferably an in situ reducing agent.

Typical coating compositions M1 are described, for example, in Schlesinger et al. "Modern Electroplating" (5th edition, 2010, John Wiley & Sons Inc., ISBN 978-0-470-16778-6) on page 451 .

Preferably, the plastic surface or the plastic molding from step d) is coated with a metal layer consisting of nickel, copper, chromium or alloys thereof, more preferably of nickel or a nickel alloy.

Preferably, the metal salt is selected from nickel, copper and chromium salts, for example halides or sulfates. Preferably, the coating composition M1 comprises at least one nickel salt, for example nickel sulfate.

The concentration of the at least one metal salt, especially of the at least one nickel salt, in the coating composition M1 is typically in the range from 15 to 35 g/L.

The pH of the coating composition M1 is typically in the range from 4 to 1 1. In principle, according to the type of buffer system, a distinction may be made between acidic or alkaline compositions. In the case of the acidic methods, the pH of the coating composition M1 is typically in the range from 4 to 7, preferably 4 to 6. In the case of alkaline methods, the pH is typically in the range from greater than 7 to 1 1 , preferably 8 to 10. Preferably, the pH is set to about 9.

Preferably, the coating composition M1 comprises at least one reducing agent, especially an in situ reducing agent, selected from the group consisting of hydrogen peroxide, peroxides, hypophosphites, hypophosphates (e.g. sodium hypophosphate), borane and borane derivatives (e.g. aminoborane such as dimethylaminoborane, sodium borohydride) and hydrazine.

The concentration of reducing agent in the coating composition M1 is typically 15 to 30 g/L.

Typically, the coating composition M1 for chemical nickel baths may comprise typical further components and additives known to those skilled in the art, as described, for example, in chapter 18.3 in Schlesinger et al. "Modern Electroplating" (5th edition, 2010, John Wiley & Sons Inc., ISBN 978-0-470-16778-6). Typically, the coating composition M1 may comprise complexing agents for the nickel ions, preferably carboxylic acids and hydroxycarboxylic acids, for example succinic acid, citric acid, malic acid, tartaric acid and/or lactic acid, and acetic acid, propionic acid, maleic acid, fumaric acid and/or itaconic acid. Buffers used may typically be citrates, acetates, phosphates and ammonium salts.

Typically, the coating composition M1 used may be a standard commercially available coating bath for electroless nickel deposition, for example "Electroless Nickel 601 KB" from HSO or "Surtec 3/1 1 D" from Surtec.

The temperature of the coating composition M1 during the performance of step d) in the case of acidic processes is typically 60 to 100°C and in the case of alkaline processes typically in the range from 25 to 50°C.

Step f)

Step f) of the process of the invention, finally, comprises the electrochemical deposition of metal layers, preferably of one or more layers consisting essentially of nickel, copper and/or chromium. Step f) may especially comprise one, two or more than two different electrochemical coatings.

By the process of the invention, it is possible to improve the adhesion of the metal layers, especially of the chemically deposited nickel layer described and of the subsequent

electrochemically deposited nickel, copper and chromium layer, to plastic surfaces, for example made from ABS, or to actually make said adhesion possible at all for many plastics. The achieved adhesion of the metal layers is very good, even in the event of mechanical stress or high temperatures. In addition, the metal surfaces obtained by the process of the invention have a particularly advantageous regular structure.

The process of the invention comprises, in step f), the electrochemical coating of the plastic surface, especially the plastic molding, from step e) with at least one further metallic layer, by electrochemically treating the plastic surface, especially the plastic molding, from step e) with at least one coating composition M' comprising at least one metal compound.

Preferably, step f) comprises the electrochemical coating of the plastic surface, especially the plastic molding, with at least one metallic layer consisting essentially of copper. For this purpose, the plastic surface, especially the plastic molding, is subjected to an electrochemical electrolysis with a coating composition M2 comprising at least one copper compound, preferably at least one copper(ll) salt.

Preferably, step f) comprises the electrochemical coating of the plastic surface, especially the plastic molding, with at least one metallic layer consisting essentially of chromium. For this purpose, the plastic surface, especially the plastic molding, is preferably contacted with a coating composition M3 comprising at least one chromium compound, preferably selected from chromic acid, chromic acid derivatives, chromium(VI) salts and chromium(lll) salts, and subjected to an electrochemical electrolysis. Preferably, the invention relates to a process as described above, wherein the electrochemical coating in step f) comprises (and preferably consists of) the following steps: electrochemically coating the surface, especially the plastic molding, from step e) with a layer consisting essentially of copper and/or nickel, by treating the surface, especially the plastic molding, from step e) with a coating composition M2 comprising at least one copper compound, especially a Cu(ll) salt, and/or at least one nickel compound, especially an Ni(ll) salt; and electrochemically coating the surface, especially the plastic molding, from step f1 ) with a layer consisting essentially of chromium, by treating the surface, especially the plastic molding, from step f1 ) with a coating composition M3 comprising at least one chromium compound, especially comprising at least one chromium compound selected from chromic acid, chromic acid derivatives, chromium(VI) salts and chromium(lll) salts.

Preferably, in step f1 ), the surface from step e) is electrochemically coated with a layer consisting essentially of copper, by treating the surface from step e) with a coating composition M2 comprising at least one copper compound, especially comprising at least one Cu(ll) salt. Further preferably, in step f1 ), the surface from step e) is electrochemically coated with one or more layers consisting essentially of copper and one or more layers consisting essentially of chromium. Preferred coating sequences (steps e), f1 ) and f2)) may be as follows: Ni (chem)→ SB-Ni→ B-Ni→ Cr or Ni (chem)→ Cu→ SB-Ni→ B-Ni→ Cr or Cu (chem)→ SB-Ni→ B-Ni→ Cr or Cu (chem)→ Cu→ SB-Ni→ B-Ni→ Cr; where SB-Ni is a semibright nickel layer and B-Ni is a bright nickel layer. Typically, the coating composition M2 comprises at least one copper salt, preferably at least one copper(ll) salt, for example copper sulfate (CuSC ). Typically, the coating composition M2 comprises at least one copper salt, water and an acid, for example sulfuric acid, alkylsulfonic acids such as methane sulfonic acid. Typically, the coating composition M2 may comprise as a further additive an additive customary for this application, for example a surfactant, a brightener, suppressors or levellers.

Typically, the coating composition M2 used may be a standard commercially available copper electrolysis bath, for example "Copper HD 500" from HSO or "Surtec 867" from Surtec.

Typically, the coating composition M3 comprises at least one chromium salt and/or chromic acid, preferably at least one chromium(lll) salt and/or one chromium(VI) salt, more preferably chromic acid hbCrC and/or chromium trioxide CrC"3. Typically, the coating composition M3 comprises at least one chromium compound, especially chromic acid, water and an acid as catalyst, for example at least one acid selected from sulfuric acid (H2SO4), hydrofluoric acid (HF), hexafluorosilicic acid (H2S1F6), alkylsulfonic acids such as methane sulfonic acid.

Typically, the coating composition M3 may comprise, as further additive, a surfactant known for this application.

The process of the invention may comprise one or more rinse steps, in each case before and/or after the steps a) to f) described. Especially after step f), the plastic surfaces, especially the plastic moldings, may be rinsed, preferably rinsed with water, and/or dried. Description of the figure

The electron micrographs in figure 1 show ABS surfaces which have been obtained according to comparative example C1 (with a simple rinse step) (upper image) and ABS surfaces which have been obtained according to inventive example 11 with ultrasound treatment according to the invention (lower image). In examples C1 and 11 , an etchant composed of MTBS:EMIM-OAc (95:5) was used. The ABS surfaces were etched at 70°C for 10 min.

Figure 2 shows one possible configuration of steps a) and b) of the invention. The labels here have the following meanings:

(I) pretreatment bath (step a)

(II) collecting vessel of the spray apparatus (step b1 )

(III) spray nozzles (step b1 )

(IV) ultrasound rinse bath (step b2)

(V), (VI) filters

(1 ) onward route of the molding to (II)

(2) onward route of the molding to (IV)

(3) removal of the spray solution, first spray solution

(4) removal of the ultrasound bath rinse solution, second rinse solution

(5) onward route of the cleaned rinse solutions

(5.1 ), (5.2) recycling of the cleaned rinse solution to (II)/ (IV)

(6.1 ), (6.2) discharge of the plastic removed

(7) discharge of a portion of the cleaned rinse solution

Figure 2 shows one embodiment of process steps a), b1 ) and b2). The molding is immersed into the treatment bath (I) comprising at least one ionic liquid IL (step a). When the molding is moved onward via (1 ) to the spray step (spray apparatus consisting of (II) and (III)), a portion of the ionic liquid and partly dissolved plastic particles on the surface of the molding are entrained therewith. In the spray apparatus (collecting vessel (II) and spray nozzles (III)), adhering composition C is rinsed off the molding by spraying the molding with the first rinse solution RS (step b1 ). The spent rinse solution is collected in the collecting vessel and conducted via (3) to the filter (VI). When the molding is moved onward via (2) to the ultrasound rinse bath (IV) comprising the second rinse solution RS (step b2)), a portion of the ionic liquid and of the first rinse solution and partly dissolved plastic particles on the surface of the molding are again entrained therewith. The molding is immersed into the ultrasound bath, removed from the bath after the dwell time and sent to the further process steps. In the ultrasound bath (IV), in a continuous manner, the second rinse solution is removed from the bath via (4) and fed to the filter (V). In addition, there is a feed of cleaned rinse solution via (5), (5.1 ) and (5.2) to (II) and (IV). In the filters (V) and (VI), the polymer is filtered out of the spent rinse solutions and discharged. The cleaned rinse solutions are recycled via (5) to the process; a portion is discharged via (7).

The invention is illustrated in detail by the examples which follow. Example 1

1 .1 General test method for examination of etching action

A plaque of dimensions 60 x 30 x 2 mm of ABS (acrylonitrile/butadiene/styrene terpolymer Terluran® GP 35 from Styrolution) is immersed at 70°C into 2 L of stirred ionic liquid

(composition C) for 10 minutes. After the etching has ended, the substrate is rinsed with water. In the inventive example, the plaque is subsequently treated in an ultrasound water bath.

The etching action is checked by means of SEM analysis and shows new structuring of the surface (see figure 1 ).

1 .2 Comparison of the etching outcome with and without an ultrasound rinse step

The etching steps were conducted as described above on ABS test plaques, using an etch solution composed of methyltri(1 -butyl)ammonium methylsulfate (MTBS) and 1 -ethyl-3- methylimidazolium acetate (EMIM-OAc) in an MTBS/EMIM weight ratio of 95:5.

After the etching step (step a)), the ABS test plaques were either immersed into a water bath at 50°C for 10 min (C1 ) or treated with ultrasound (6 L of water, 280 W, corresponding to about 50 W/L, at 35 kHz) at 50°C for 10 min (11 ).

The SEM images in figure 1 show the ABS surfaces which have been obtained according to comparative example C1 (with a simple rinse step) (upper image) and the ABS surfaces which have been obtained according to inventive example 11 with ultrasound treatment according to the invention (lower image).

In the SEM images, it is apparent that the ultrasound rinsing step gave much better removal of partly dissolved plastic particles which were partly dissolved by the etch solution. In the SEM image C1 without ultrasound treatment, voluminous porous plastic residues are clearly apparent. In the SEM image 11 with ultrasound treatment, such residues are entirely absent. The SEM image with ultrasound treatment shows a homogeneously etched ABS surface having a morphology of particularly good suitability for conduction of subsequent metallization steps. Example 2 - Variation of etch conditions

ABS test plaques were treated by the general test method described above for examination of etching action. The etch solution (composition C) used in all cases was a mixture of methyltri(1 - butyl)ammonium methylsulfate (MTBS), 1 -ethyl-3-methylimidazolium ethylsulfate (EMIM-EtS0₄) and propylene carbonate (PC) in an MTBS/EMIM-ETS0₄/PC weight ratio of 80:10:10. Various etch conditions (temperature and time) as described in table 2 below were established. The etching action was checked by means of SEM analysis and shows new structuring of the surface.

After the etching and rinsing, the test plaques were metallized. For this purpose, the following treatment steps were conducted:

Treatment with activator composition A -> treatment with accelerator composition B -> chemical electroless deposition of nickel using the coating composition M1 ->

electrodeposition of copper using the coating composition M'. The following products were used:

Activator composition A "Activator U" from HSO or "Surtec 961 Pd" from Surtec

Accelerator composition B "HSO Accelerator" from HSO or "Surtec 961 A" from

Surtec

Coating composition M1 "Electroless Nickel 601 KB" from HSO or "Surtec

3/1 1 D" from Surtec

Coating composition M' "Copper HD 500" from HSO or "Surtec 867" from

Surtec The quality of the metal coating is determined with the aid of what is called the cross-cut test according to ISO 2409:2007. The results are summarized in table 1 .

Table 1 : Etch conditions (step a))

Experiment Temperature Treatment Cross-cut test

No. time

[°C] [min]

P1 45 15 inadequate adhesion

P2 50 5 adhesion P3 50 7 adhesion

P4 50 10 adhesion

P5 65 5 inadequate adhesion

P6 65 7 inadequate adhesion

It is found that, by means of a treatment of the ABS surface in step a) at a temperature of 45°C, even with an etch time of 15 min, it is not possible to obtain homogeneous structuring of the surface (P1 ). When the etch temperature is too low and/or the treatment time is too short, the surface is insufficiently roughened. The nucleation necessary for the metallization in the subsequent step is inadequate. It is not possible to produce a layer between the plastic surface and metal layers that has adequate adhesion (insufficient "push-button effect").

At a higher etch temperature of 65°C and/or with an excessively long etch time, the plastic surface is attacked excessively (P5 and P6), meaning that the surface is too fissured and exhibits inhomogeneous structuring.

A particularly advantageous and homogeneous surface structuring of the ABS surface was obtained in this example at a temperature in the range from 50 to 60°C, more preferably 50 to 55°C, and with a duration of 5 to 15 min (see P2 to P4). In the case of optimal etch parameters, the depressions (also called caverns) necessary for the "push-button effect" are formed, and the subsequent metal layers have good adhesion. The optimal etch conditions, such as time and temperature, may vary according to the type of plastic, geometry, injection molding parameters or age of the substrate.

Claims

A process for coating a plastic surface with metals, comprising the steps of a) pretreating the plastic surface with a composition C (etch solution) comprising at least one ionic liquid IL; b) treating the plastic surface from step a) with an aqueous rinse solution RS while applying ultrasound; c) treating the plastic surface from step b) with an activator composition A comprising at least one ionogenic and/or colloidal activator; d) treating the plastic surface from step c) with an accelerator composition B

comprising an acid and/or a reducing agent; e) chemically depositing a metal layer, by treating the plastic surface from step d) with a coating composition M1 comprising at least one metal salt and at least one reducing agent; f) electrochemically coating the surface from step e) with at least one further metal layer, by electrochemically treating the surface from step e) with at least one coating composition M' comprising at least one metal compound.

The process according to claim 1 , wherein the ionic liquid IL is a salt which is liquid at 100°C, 1 bar.

The process according to either of claims 1 and 2, wherein at least one ionic liquid IL is at least one salt having a cation selected from imidazolium cations, pyridinium cations, pyrazolium cations and alkylammonium cations.

The process according to any of claims 1 to 3, wherein at least one ionic liquid IL is a salt having an alkylammonium cation of formula (I).

R

I ₊

N-

I

R

(i)

wherein is an unbranched and unsubstituted Ci-Cis-alkyl, CHsCKChbCI-bC CI-bCI- - CH₃CH20-(CH2CH20)p-CH₂CH2- with p = 0 to 3; R¹, R² and R³ are each independently: a hydrogen atom, unsubstituted Ci-Cis-alkyl, 2-hydroxyethyl, 2-cyanoethyl, 2- (methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, chlorine, CH₃0-(CH2CH20)p-CH₂CH2- or CH₃CH20-(CH2CH20)p-CH₂CH2- with p = 0 to 3, or two adjacent R¹, R² and R³ radicals together with the nitrogen atom in formula (I) are a saturated unsubstituted five- to seven-membered ring;

X is an anion; and n is 1 , 2 or 3.

The process according to any of claims 1 to 4, wherein at least one ionic liquid IL is methyltri(1 -butyl)ammonium methylsulfate (MTBS).

The process according to any of claims 1 to 5, wherein the ionic liquid IL is a

combination of at least one first ionic liquid IL1 and at least one second ionic liquid IL2, the first ionic liquid IL1 comprising, as cation, at least one alkylammonium cation and the second ionic liquid IL2 comprising, as cation, at least one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom.

The process according to any of claims 1 to 6, wherein the composition C comprises at least one ionic liquid IL selected from the group consisting of methyltri(1 -butyl)ammonium methylsulfate, 1 -ethyl-3-methylimidazolium methylsulfate, 1 -ethyl-3-methylimidazolium ethylsulfate, 1 -ethyl-3-methylimidazolium hydrogensulfate, 1 -ethyl-3-methylimidazolium thiocyanate, 1 -ethyl-3-methylimidazolium acetate, 1 -ethyl-3-methylimidazolium

methanesulfonate and 1 -ethyl-3-methylimidazolium diethylphosphate.

The process according to any of claims 1 to 7, wherein the composition C comprises 1 % to 30% by weight, based on the overall composition C, of at least one solvent S selected from the group consisting of water, propylene carbonate, polyethylene glycols, diacetin, triacetin, ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol.

The process according to any of claims 1 to 8, wherein the composition C comprises

49% to 94% by weight, based on the overall composition C, of at least one ionic liquid IL1 comprising at least one alkylammonium cation;

5% to 50% by weight, based on the overall composition C, of at least one ionic liquid IL2 comprising, as cation, at least one aromatic heterocycle having a delocalized cationic charge and comprising at least one nitrogen atom; and 1 % to 30% by weight, based on the overall composition C, of at least one solvent S selected from the group consisting of water, propylene carbonate, polyethylene glycols, diacetin, triacetin, ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol.

10. The process according to any of claims 1 to 9, wherein the plastic surface is one

consisting of or comprising polyamides, polystyrenes or copolymers of styrene selected from styrene/acrylonitrile copolymers, acrylic ester/styrene/acrylonitrile copolymers and acrylonitrile/butadiene/styrene copolymers, or blends and/or multicomponent plastics comprising at least one of the plastics mentioned.

1 1. The process according to any of claims 1 to 10, wherein the metals comprise at least one metal selected from nickel, aluminium, copper, chromium, tin, zinc and alloys thereof.

12. The process according to any of claims 1 to 1 1 , wherein the plastic surface is one

consisting of or comprising acrylonitrile/butadiene/styrene copolymer, in which case the pretreatment of the plastic surface with the composition C in step a) is effected at a temperature in the range from 50 to 60°C and over a period of 5 to 15 min.

13. The process according to any of claims 1 to 12, wherein the treatment of the plastic

surface with the aqueous rinse solution RS while applying ultrasound in step b) is effected by dipping the plastic surface from a) into an ultrasound bath comprising the aqueous rinse solution RS at a power in the range from 40 to 60 watts/L, over a period of 1 to 30 min and at a temperature of 40 to 60°C, and wherein the aqueous rinse solution RS comprises at least 85% by weight of water.

14. The process according to any of claims 1 to 13, wherein step b) comprises the following steps: b1 ) treating the plastic surface from step a) with a first aqueous rinse solution RS1 , by spraying the plastic surface with the first aqueous rinse solution RS1 or dipping it into the first aqueous rinse solution RS1 ; b2) treating the plastic surface from step b1 ) with a second aqueous rinse solution RS2 while applying ultrasound.

15. The process according to any of claims 1 to 14, wherein the electrochemical coating in step f) comprises the following steps: f1 ) electrochemically coating the surface from step e) with a layer consisting essentially of copper and/or nickel, by treating the surface from step e) with a coating composition M2 comprising at least one copper compound and/or at least one nickel compound; and f2) electrochemically coating the surface from step f1 ) with a layer consisting essentially of chromium, by treating the surface from step f1 ) with a coating composition M3 comprising at least one chromium compound.