EP2928984A1

EP2928984A1 - Process for metallizing nonconductive plastic surfaces

Info

Publication number: EP2928984A1
Application number: EP13799621.1A
Authority: EP
Inventors: Leonas Naruskevicius; Danas Budilovskis; Ona GYLIENE; Loreta TAMASAUSKAITE TAMASIUNAITE
Original assignee: Atotech Deutschland GmbH and Co KG
Current assignee: Atotech Deutschland GmbH and Co KG
Priority date: 2012-12-07
Filing date: 2013-12-06
Publication date: 2015-10-14
Also published as: CA2893664A1; KR20170039775A; CN104854216A; LT6070B; WO2014087004A1; CA2893664C; US20150307992A1; JP2015537122A; BR112015012930A2; KR20150093214A; LT2012110A

Abstract

The present invention relates to a process for metallizing nonconductive plastics using an etching solution free of hexavalent chromium. The etching solution is based on an sulphuric acidic solution comprising a source of chlorate ions and a vanadium compound. After the treatment of the plastics with the etching solution, the plastics are metallized by means of known processes.

Description

Process for metallizing nonconductive plastic surfaces

Field of the invention

The invention regards the pretreatment of nonconductive plastic surfaces prior to their metallization and may be applied in various industries where decorative or functional metal coating of plastic parts is required. The pretreatment is performed in a solution free of hexavalent chromium which contains an oxidising agent and a stabiliser compound.

Background of the invention

A conventional method of pretreatment of nonconductive plastic surfaces prior to their electroless metallization, mostly electroless nickel-plating or copper-plating, consists of etching the surface in hexavalent chromium containing solution, followed by the activation in a ionic or colloidal solution of palladium compounds and either the reduction in the sodium hypophosphite solution (in most cases) or the acceleration in an acidic solution (usually hydrochloric acid) of the palladium ions or colloidal palladium particles, respectively, adsorbed on the plastic surface.

Etching during the pretreatment step of the nonconductive substrate surface is required for hydrophilisation purposes so that the surface becomes hydrophilic in other phases of the process in water solutions, with sufficient quantities of palladium salts adsorbed, and for ensuring proper binding of the metal coating to the nonconductive plastic surface. The activation with the subsequent reduction or acceleration is performed in order to initiate the electroless deposition of the metal on the plastic. Thereafter, electroless plating with metal in the metallization solution takes place through auto-catalytic reactions where the metal deposited on the surface acts as a catalyst for further depositing. The metals nickel and copper are mostly used for this electroless plating.

Thereafter, electrolytic or galvanic plating can be performed on the first metal layer. Various metals can be applied, for example chromium, nickel, copper and brass or other alloys of the foregoing metals.

The main shortcomings of the conventional method are related to the cancerogenicity of the chromic acid in the etching solution. Furthermore, the metal deposited during the electroless deposition step, for example nickel, also covers parts of rack insulated with plastisol, which results in the metal losses in the solutions of subsequent metal plating electrochemically and therefore is undesired. Various methods to overcome this problem have been suggested in the prior art.

US Patent Application No. 2005/0199587 A1 discloses a method of etching of nonconductive plastic surfaces in an acidic solution containing 20-70 g/l of potassium permanganate. Optimal KMn0₄ concentration in above mentioned solution is close to 50 g/l. When the concentration is below 20 g/l, the solution is ineffective, with the upper concentration limit determined by the solubility of potassium permanganate. The etching is followed by the activation in a palladium salt solution containing amine and by further reducing treatment, e.g. in a borohydride, hypophosphite or hydrazine solution.

This method, however, has substantial shortcomings. At high permanganate concentrations in the etching solution (recommended approx. 50 g/l, with phosphoric acid approx. 48 vol.%), it decomposes very quickly, in particular at high temperatures. The recommended temperature is 100°F, i.e. 37°C. Tests have shown that at this temperature the solution becomes ineffective after 4 to 6 hours, i.e. the plastic surface is not hydrophilicated and remains uncoated at some places during metallization; in the coated areas, adhesion with the plastic is very weak. Often adjustments of the solution with new portions of permanganate, which is not cheap, are required. Furthermore, insoluble permanganate decomposition products are formed, contaminating the surface being metallized.

Furthermore, etching in the permanganate solutions activates the surface of the rack's plastisol insulation as it is coated with the product of the etching reaction, i.e. manganese dioxide. The latter stimulates adsorption of palladium compounds on plastisol, which tends to metallize in the solutions of electroless metal deposition. Formation of manganese dioxide on surfaces is characteristic of the permanganate etching solutions of any composition. Therefore, a very important objective of the present invention is to avoid rack metallization and resulting metal losses in the subsequent metallisation stage.

Lithuanian patent application number LT 2008-082 also concerns the pretreatment of nonconductive plastic surfaces prior to metallisation. Disclosed is a pretreatment composition for etching e.g. polyimide for 1 - 2 minutes with a temperature of 10 - 80 °C, 0,005 - 0,2M oxidizing solution in sulphuric acid in a concentration of between 13 mol/L (about 75 vol.%) and 17 mol/L (about 90 vol.%), wherein the oxidizers can be KMn0₄, HCI0₄, V₂0₅, KCI0₃. In case of a chlorate (CI0₃ ^~, M = 83.5 g/mol), this corresponds to a concentration of between 0.4 - 16.7 g/l.

An example is provided in this application in the Table 2 which contains 7 mol/L (about 50 vol.%) sulphuric acid and 0.2 mol/L (16.7 g/L) chlorate. It has been shown, however, that such high chlorate at concentrations result in rapid decomposition of the pretreatment solution which is undesired.

Lithuania Invention Application No. 2012 042 relates to a method of etching of plastics in a chlorate solution in 50 to 80 vol.% sulphuric acid. Apart from chlorate, the etching solution can also contain another oxidizer with a standard oxidizing potential exceeding that of the chlorate ions. Upon treatment in the alkali metal hydroxide solution, the plastic is activated in a solution of palladium compounds, then held in a solution for the purpose of either reduction or acceleration and afterwards subjected to an electroless nickel-plating process. The advantages of the method consist in the high values of adhesion between the electroless nickel coating and the plastic as well as in the exclusion of the plastisol- coated plastic coated rack from the nickel-plating process.

The etching solution may absorb water vapour from the ambient air and, due to resulting dilution, the etching properties might negatively be influenced. One solution to this problem is the increase of temperature of the etching solution, which might, however, result in lower stability of the solution.

Description of the invention

It is therefore an object of the present invention to find etching solutions for the pretreatment of electrically nonconductive plastic surfaces of articles, which have an increased stability at elevated temperatures and still provide sufficient adhesion strength of the metal layers applied on the plastic surface.

This purpose is achieved by using an etching solution for the pretreatment of electrically nonconductive plastic surfaces comprising the following components:

a) one or more chlorate ion sources,

b) one or more vanadium compounds,

c) sulphuric acid.

The source of chlorate ions can be any water soluble salt. Most commonly used are sodium and potassium chlorate.

The concentration of the chlorate ions in the etching solution ranges between 0.0016 mol/l and up to 0.12 mol/l. Preferred ranges vary between 0.003 mol/l and 0.08 mol/l or between 0.01 mol/l and 0.06 mol/l or 0.004 mol/l and 0.04 mol/l.

The concentration of the sulphuric acid ranges between 50 and 80 vol.%, preferably between 55 and 70 vol.% and even more preferred between 60 and 65 vol.%. The concentration of the vanadium compound ranges between 0.01 and 20.0 g/l, preferentially from 0.1 to 8 g/l, and even more preferentially from 0.5 to 7.0 g/l, in the etching solution. Upon employing the vanadium compound, higher temperatures can be used in the etching process retaining the strong adhesion between the plastic surface and the newly formed metal layer. It is also advantageous and known to those skilled in the art that upon raising the temperature of the etching solution the concentration of the sulphuric acid therein can be decreased making the etching solution both cheaper and safer to use.

As vanadium compounds any water soluble vanadium compound may be used. Most commonly used are divanadium pentoxide (V₂0₅) and / or alkali vanadates, like e.g. NaV0₃, KV0₃.

Optionally, phosphoric acid as an additional acid can be comprised in the etching solution. The concentration of the phosphoric acid typically ranges from 10 to 40 vol.%, preferably between 15 and 30 vol.%. When phosphoric acid is additionally being used, the adhesion of the plated metal layer can surprisingly additionally be increased.

A mixture of between 60 and 65 vol.% sulphuric acid and 20 and 30 vol.% phosphoric acid is particularly preferred.

The etching solution can optionally contain 2 to 20 g/l of additional oxidizer, with the standard oxidising potential exceeding that of the chlorate ions. Such oxidizers are preferentially periodate sources, like e.g. sodium periodate.

The chlorate, the vanadium compound and sulphuric acid form a yellow compound, the normal oxidising potential of which in the H₂S0₄ solution medium is sufficient for the reaction with the plastic surface at room temperature. Due to this reaction, the plastic surface becomes hydrophilic and adsorbs the palladium compounds with sufficient strength. The yellow colour product of the reaction between chlorate and the sulphuric acid is a poison for palladium catalyst. During etching, it penetrates the surface layers of the rack's plastisol insulation and prevents electroless metal deposition on plastisol in the electroless metallisation solutions; the metallization process taking place on the nonconductive plastic surface is not affected.

The etching solution can be prepared as follows:

The concentrated sulphuric acid is mixed with deionised water. The solution is left to cool down. Then the chlorate ion source, the vanadium compound and optionally a second oxidizer are dissolved in the solution. The etching solution is ready for use. When the quantity of water used for the preparation of the etching solution exceeds 50% by volume compared with the sulphuric acid, no yellow plastic-oxidising compound is formed between the chlorate ions, the vanadium compound and the sulphuric acid molecules, therefore, the water content of the solution preferably should not exceed 50% by volume.

When the quantity of water used for the preparation of the etching solution is less than 20% by volume compared with the sulphuric acid, the surface of plastics is decomposed during etching due to too high concentration of sulphuric acid, therefore, no adhesion between the chemical nickel coating and the plastic is obtained.

If the quantity of chlorate ion source dissolved in the etching solution is smaller than 0.5 g/l, the etching process takes longer than 15 min., therefore, such concentration is not acceptable.

If the quantity of chlorate ion source dissolved in the etching solution exceeds 5.0 g/l, over-etching may be observed after the minimum etching period, i. e. 2 to 3 min., which results in a much weaker adhesion strength, due to which such high concentration of chlorate is not acceptable either. However, depending on the substrate material, higher concentrations of up to 15 g/l may be acceptable resulting in sufficient adhesion.

If the concentration of the vanadium compound exceeds 8.0 g/l, the adhesion begins to deteriorate and, thus, should not be increased any further. When lowering the concentration of the vanadium compound below 0.1 g/l, the adhesion is being impaired and, therefore, should be kept higher.

The inventive etching solution preferably does not contain any chromium or chromium compounds; the etching solution contains neither chromium(lll) ions nor chromium(VI) ions. The inventive etching solution is thus free of chromium or chromium compounds; the etching solution is free of chromium(lll) ions and chromium(VI) ions.

The objective of the present invention is further achieved by the following process according to the invention:

Process for metallizing electrically nonconductive plastic surfaces of articles, comprising the process steps of:

A) etching the plastic surface with an aqueous etching solution;

B) treating the plastic surface with a solution of a metal colloid or of a compound of a metal, the metal being selected from the metals of transition group I of the Periodic Table of the Elements and transition group VIII of the Periodic Table of the Elements, and

C) metallizing the plastic surface with a metallizing solution;

characterized in that the etching solution comprises at least a source of chlorate ions, sulphuric acid and a vanadium compound. The concentrations and procedures given for the inventive etching solution stated above apply for this purpose described hereinafter as well.

An important distinctive feature of the proposed method that makes it different from the state of the art is that it allows for good adhesions of plastic surface and deposited metal layer to be obtained at elevated temperatures. Another beneficial aspect of the invention lies in the removal of fats and oils which are often present on plastic surfaces from prior processing steps and, thus, making the etching process even more effective.

For the etching of the plastic surface in the application as the method of treatment of the plastic surface prior to its electroless metallization consisting of the etching of the plastic by means of an inorganic acid solution with an oxidizer, activation by the palladium salt solution, and treatment by either reducing or accelerating solution. The temperature for the etching process ranges from 20 to 65 °C, preferred from 30 to 65 °C, even more preferred from 40 to 65 °C.

The etching time varies with the substrate material and its shape and can be determined by routine experiments. Generally, it varies between 1 and 20 minutes, preferably not longer than 10 minutes.

Articles in the context of this invention are understood to mean articles which have been manufactured from at least one electrically nonconductive plastic or which have been covered with at least one layer of at least one electrically nonconductive plastic. The articles thus have surfaces of at least one electrically nonconductive plastic. Plastic surfaces are understood in the context of this invention to mean these said surfaces of the articles.

The process steps of the present invention are performed in the sequence specified, but not necessarily in immediate succession. It is possible for further process steps and additionally rinse steps in each case, preferably with water, to be performed between the steps. The plastic surfaces have been manufactured from at least one electrically nonconductive plastic. In one embodiment of the present invention, the at least one electrically nonconductive plastic is selected from the group consisting of an acrylonitrile-butadiene- styrene copolymer (ABS copolymer), a polyamide (PA), a polycarbonate (PC) and a mixture of an ABS copolymer with at least one further polymer.

In a preferred embodiment of the invention, the electrically nonconductive plastic is an ABS copolymer or a mixture of an ABS copolymer with at least one further polymer. The at least one further polymer is more preferably polycarbonate (PC), which means that particular preference is given to ABS/PC mixtures.

In a further preferred embodiment of the invention, the following further process step is performed between process steps A) and B):

A i) treating the plastic surface in a solution comprising an alkaline solution. The further process step A i) is also referred to as neutralizing treatment. Any source of alkalinity can be used, sources of hydroxide ions such as aqueous solutions of sodium hydroxide are preferred.

In a further alternative embodiment of the invention, the following further process step is performed between process steps A) and B):

A i) treating the plastic surface in a solution comprising a reducing agent for chlorate ions and optionally a second oxidizer.

The further process step A i) is also referred to as reduction treatment. This reduction treatment reduces chlorate ions and optionally a second oxidizer adhering to the plastic surfaces and facilitates removal of such ions. The reducing agent is for example selected from the group consisting of hydroxylammonium sulphate, hydroxylammonium chloride and hydrogen peroxide. The process of the present invention further comprises process step B), in which a plastic surface is treated with a solution of a metal colloid or of a compound of a metal.

The metal of the metal colloid or of the metal compound is selected from the group comprising the metals of transition group I of the Periodic Table of the Elements (PTE) and transition group VIII of the PTE.

The metal of transition group VIII of the PTE is selected from the group comprising palladium, platinum, iridium, rhodium and a mixture of two or more of these metals. The metal of transition group I of the PTE is selected from the group comprising gold, silver and a mixture of these metals. A preferred metal in the metal colloid is palladium. The metal colloid is stabilized with the protective colloid. The protective colloid is selected from the group comprising metallic protective colloids, organic protective colloids and other protective colloids. As a metallic protective colloid, preference is given to tin ions. The organic protective colloid is selected from the group comprising polyvinyl alcohol, polyvinylpyrrolidone and gelatine, preferably polyvinyl alcohol.

In a preferred embodiment of the invention, the solution of the metal colloid in process step B) is an activator solution with a palladium/tin colloid. This colloid solution is obtained from a palladium salt, a tin(ll) salt and an inorganic acid. A preferred palladium salt is palladium chloride. A preferred tin(ll) salt is tin(ll) chloride. The inorganic acid may consist in hydrochloric acid or sulphuric acid, preferably hydrochloric acid. The colloid solution forms through reduction of the palladium chloride to palladium with the aid of the tin(ll) chloride. The conversion of the palladium chloride to the colloid is complete; therefore, the colloid solution no longer contains any palladium chloride. The concentration of palladium is 5 mg/l - 100 mg/l, preferably 20 mg/l - 50 mg/l and more preferably 30 mg/l - 45 mg/l, based on Pd²⁺. The concentration of tin(ll) chloride is 0.5 g/l - 10 g/l, preferably 1 g/l - 5 g/l and more preferably 2 g/l - 4 g/l, based on Sn²⁺. The concentration of hydrochloric acid is 100 ml/l - 300 ml/l (37% by weight of HCI). In addition, a palladium/tin colloid solution additionally comprises tin(IV) ions which form through oxidation of the tin(ll) ions. The temperature of the colloid solution during process step B) is 20 °C - 50°C and preferably 35 °C - 45°C. The treatment time with the activator solution is 0.5 min - 10 min, preferably 2 min - 5 min and more preferably 3 min - 5 min.

In a further embodiment of the invention, in process step B), the solution of a compound of a metal is used in place of the metal colloid. The solution of a metal compound used is a solution comprising an acid and a metal salt. The metal in the metal salt consists in one or more of the above-listed metals of transition groups I and VIII of the PTE. The metal salt may be a palladium salt, preferably palladium chloride, palladium sulphate or palladium acetate, or a silver salt, preferably silver acetate. The acid is preferably hydrochloric acid. Alternatively, it is also possible to use a metal complex, for example a palladium complex salt, such as a salt of a palladium-aminopyridine complex. The metal compound in process step B) is present in a concentration of 40 mg/l to 80 mg/l, based on the metal. The solution of the metal compound can be employed at a temperature of 25 °C to 70 °C, preferably at 25 °C. The treatment time with the solution of a metal compound is 0.5 min - 10 min, preferably 2 min - 6 min and more preferably 3 min - 5 min.

Between process steps A) and B), the following further process step can be performed: A ii) treating the plastic surface in an aqueous acidic solution.

Preference is given to performing process step A ii) between process steps A i) and B). If, in the process according to the invention, process step A i) was followed by the protection of the racks, process step A ii) is more preferably performed between the protection of the racks and process step B).

The treatment of the plastic surfaces in process step A ii) is also referred to as preceding dipping, and the aqueous acidic solution used as a preceding dipping solution. The preceding dipping solution has the same composition as the colloid solution in process step B), without the presence of the metal in the colloid and the protective colloid thereof. The preceding dipping solution, in the case of use of a palladium/tin colloid solution in process step B), comprises exclusively hydrochloric acid if the colloid solution likewise comprises hydrochloric acid. For preceding dipping, brief immersion into the preceding dipping solution at ambient temperature is sufficient. Without rinsing the plastic surfaces, they are treated further directly with the colloid solution of process step B) after the treatment in the preceding dipping solution. Process step A ii) is preferably performed when process step B) involves the treatment of a plastic surface with a solution of a metal colloid. Process step A ii) can also be performed when process step B) involves the treatment of a plastic surface with a solution of a compound of a metal. After the treatment of the plastic surfaces with the metal colloid or the metal compound in process step B), these can be rinsed.

In a further embodiment of the invention, the following further process steps are performed between process steps B) and C):

B i) treating the plastic surface in an aqueous acidic solution and

B ii) electrolessly metallizing the plastic surface in a metallizing solution. The embodiment is exemplified schematically in Table 1 .

Table 1 : Embodiment of plastic metallization

These further process steps B i) and B ii) are employed when the articles are to be metallized by an electroless metallization process, i.e. a first metal layer is to be applied to the plastic surfaces by an electroless process. If the activation in process step B) has been performed with a metal colloid, the plastic surfaces are treated in process step B i) with an accelerator solution in order to remove constituents of the colloid in the colloid solution, for example a protective colloid, from the plastic surfaces. If the colloid in the colloid solution in process step B) is a palladium/tin colloid, the accelerator solution used is preferably an aqueous solution of an acid. The acid is selected, for example, from the group comprising sulphuric acid, hydrochloric acid, citric acid and tetrafluoroboric acid. In the case of a palladium/tin colloid, the accelerator solution helps to remove the tin compounds which served as the protective colloid.

Alternatively, in process step B i), a reductor treatment is performed when, in process step B), a solution of a metal compound has been used in place of a metal colloid for the activation. The reductor solution used for this purpose then comprises, if the solution of the metal compound was a hydrochloric acid solution of palladium chloride or an acidic solution of a silver salt, hydrochloric acid and tin(ll) chloride. The reductor solution may also comprise another reducing agent, such as NaH₂P0₂ or else a borane or borohydride, such as an alkali metal borane or alkaline earth metal borane or dimethylaminoborane. Preference is given to using NaH₂P0₂ in the reductor solution. After the acceleration or treatment with the reductor solution in process step B i), the plastic surfaces can first be rinsed. Process step B i) and optionally one or more rinse steps are followed by process step B ii) in which the plastic surfaces are metallized electrolessly. Electroless nickel-plating is accomplished, for example, using a conventional nickel bath which comprises, inter alia, nickel sulphate, a hypophosphite, for example sodium hypophosphite, as a reducing agent, and also organic complexing agents and pH adjusters (for example a buffer). The reducing agent used may likewise be dimethylaminoborane or a mixture of hypophosphite and dimethylaminoborane.

Alternatively, it is possible to use an electroless copper bath for electroless copper-plating, the electroless copper bath typically comprising a copper salt, for example copper sulphate or copper hypophosphite, and also a reducing agent, such as formaldehyde or a hypophosphite salt, for example an alkali metal or ammonium salt, or hypophosphorous acid, and additionally one or more complexing agents such as tartaric acid, and also a pH adjuster such as sodium hydroxide. The surface thus rendered conductive can subsequently be electrolytically further metallized in order to obtain a functional or decorative surface.

Step C) of the process according to the invention is the metallization of the plastic surface with a metallization solution. The metallization in process step C) can be effected electrolytically. For electrolytic metallization, it is possible to use any desired metal deposition baths, for example for deposition of nickel, copper, silver, gold, tin, zinc, iron, lead or alloys thereof. Such deposition baths are familiar to those skilled in the art. A Watts nickel bath is typically used as a bright nickel bath, this comprising nickel sulphate, nickel chloride and boric acid, and also saccharine as an additive. An example of a composition used as a bright copper bath is one comprising copper sulphate, sulphuric acid, sodium chloride and organic sulphur compounds in which the sulphur is in a low oxidation state, for example organic sulphides or disulphides, as additives.

The effect of the metallization of the plastic surface in process step C) is that the plastic surface is coated with metal, the metal being selected from the above-listed metals for the deposition baths. In a further embodiment of the invention, after process step C), the following further process step is performed:

C i) storage of the metallized plastic surface at elevated temperature.

As in all electroplating processes in which a nonconductor is coated by wet-chemical means with metal, the adhesion strength between metal and plastic substrate increases in the first period after the application of the metal layer. At room temperature, this process is complete after about three days. This can be accelerated considerably by storage at elevated temperature. The process is complete after about one hour at 80 °C. It is assumed that the initially low adhesion strength is caused by a thin water layer which lies at the boundary between metal and nonconductive substrate and hinders the formation of electrostatic forces. The process and the underlying etching solution according to the invention thus enables, with good process reliability and excellent adhesion strength of the subsequently applied metal layers, achievement of metallization of electrically nonconductive plastic surfaces of articles at elevated temperatures. The adhesion strength of the metal layers applied to plastic surfaces reaches values of up to 1 .4 N/mm (corresponding approximately to 1 .4 kg/cm, 1 kg/cm = 0.98 N/mm) or higher.

In general, adhesion values of more than 0.8 N/mm are required for industrial applications and non-complex shaped objects are to be plated. In general, the higher the adhesion of the better the stability of the deposit is.

In addition, not just planar plastic surfaces are metallized with high adhesion strength by the process according to the invention; instead, inhomogeneously shaped plastic surfaces, for example shower heads, are also provided with a homogeneous and strongly adhered metal coating.

The treatment of the plastic surfaces by the process according to the invention is preferably performed in a conventional dipping process, by dipping the articles successively into solutions in vessels, in which the respective treatment takes place. In this case, the articles may be dipped into the solutions either fastened to racks or accommodated in drums. Fastening to racks is preferred. Alternatively, the articles can also be treated in what are called conveyor plants, by lying, for example, on trays and being conveyed continuously through the plants in horizontal direction. Working examples

The working examples described hereinafter are intended to illustrate the invention in detail. ABS (acrylonitrile-butadiene-styrene copolymer) and PC/ABS (a mixture of 45% by weight of polycarbonate and 55% by weight of acrylonitrile butadiene styrene copolymer) were etched during 5 min. in a 30-70 vol.% sulphuric acid solution containing 1 -20 g/l potassium chlorate (KCI0₃) and 1 0 g/l potassium periodate (KI0₄) as additional second oxidizer at 20°C, 40°C and 65°C, respectively, or in a similar solution under the conditions described above where 0.1 -8.0 g/l soluble vanadium compound was added to the solution.

After etching, the plastics were immersed for 2 min. in a neutralizing solution at room temperature containing 10 g/l NaOH , followed by activation in a solution of palladium compounds (5 min. at 20°C). The PdCI₂ concentration in the solution was 0.1 g/l, the solution pH was 2.7. Upon activation in the Pd solution the plastics were held during 5 min. in a solution containing 20 g/l of sodium hypophosphite, pH 9, at 60°C.

The samples were subsequently nickel-plated at 45 °C without external current for 10 minutes (Adhemax LFS, 25 from Atotech, process step B ii)) and then rinsed. Electroless nickel-plating was additionally followed by electrolytic copper-plating for 70 minutes (Cupracid HT from Atotech, 3.5 A/dm², room temperature, process step C)). The coating quality was evaluated by the coating/plastic adhesion strength. To evaluate the adhesion, the Ni deposit was thickened in a galvanic copper bath and the strength necessary to peel a 1 cm wide strip off the plastic was measured (kg/cm). The conditions of preparation of the plastics for the metallization and the results of the metallization (chemical nickel-plating) are presented in the table below.

Table 2: Sequence of process steps in the working example

Process step Chemistry Time Temperature

A) Etching table 2 5 min table 2

A i) Neutralization 1 0 g/l Sodium hydroxide 2 min 20 °C

B) Activation 0.1 g/l PdCI₂, pH 2.7 5 min 20 °C

B i) Reduction 20 g/l Sodium hypophosphite, pH 9 5 min 60 °C

B ii) Electroless metal

Adhemax LFS, 25 10 min 45 °C deposition C) Electrolytic metal

Cupracid HT, 3.5 A/dm² 70 min 20 °C deposition

Test pieces 1 and 2 (cf. table 3) show that an etching solution containing no vanadium compounds may be used for the etching of the ABS plastic only at room temperature. At higher temperatures of the etching solution, e.g. 40°C, the adhesion of Ni coatings on ABS deteriorated decisively. When the etching solution contained vanadium compounds (Test Pieces 3 and 4), the Ni - ABS adhesion in a solution of higher temperature was not weaker than in the case of the solution without vanadium compounds and the etching at room temperatures. Test Pieces 5, 6 and 7 showed that the same patterns relating to the presence of the vanadium compound in the etching solution applied to the etching of PC/ABS as well. As seen from Test Pieces 8, 9, 10 and 1 1 , the sulphuric acid concentration of the etching compound could be reduced to 30 vol.% under the temperature of 65°C. However, it was not worth lowering of the sulphuric acid concentration below 30 vol.% as adhesion of the Ni coating with plastics was noticeably lower even at 30 vol.%. Test Pieces 12 and 13 showed that it would be not purposeful to reduce the vanadium compound content of the etching solution below 0.1 g/l or to increase it above 8 g/l as the resulting values of the Ni coating adhesion were much lower.

In all 1 3 cases, the plastic surfaces were fully plated with Ni, with no Ni plating on plastisol-covered parts of the equipment.

Table 3: Conditions of the etching process and resulting adhesion strengths of a nickel layer on various ABS mixtures

Test Plastic H₂S0₄ KCI0₃ Etching Vanadium Adhesion piece concentration concentration temperacompound values No. in etching in etching ture, °C and its obtained, solution, solution, concentration kg/cm vol.% g/i in etching

solution, g/l

1 ABS 66 2 20 - 1 .0 - 1 .3

2 ABS 66 2 40 - 0.0 - 0.1

3 ABS 66 2 40 V2O5 O.5 1 .1 - 1 .3

4 ABS 66 2 65 V2O5 O.5 1 .3 - 1 .4 PC/ABS 66 2 20 - 0.7-0.9

PC/ABS 66 2 65 - 0.0-0.1

PC/ABS 66 2 65 V2O5O.5 0.9-1.1

ABS 40 10 65 NaV0₃1.0 1.0-1.2

PC/ABS 40 10 65 NaV0₃1.0 0.7-0.9

ABS 30 10 65 NaV0₃1.0 0.5-0.7

PC/ABS 30 10 65 NaV0₃1.0 0.3-0.5

ABS 66 2 65 V2O5O.I 1.0-1.3

ABS 66 2 65 V₂O₅8.O 0.8-1.0

Claims

1 . Etching solution for the pretreatment of electrically nonconductive plastic surfaces comprising the following components:

a) one or more chlorate ion sources,

b) one or more vanadium compounds, and

c) sulphuric acid.

2. Etching solution according to claim 1 , characterized in that the vanadium compound is divanadium pentoxide and / or alkali vanadate.

3. Composition according to any of the preceding claims, characterized in that the concentration of the vanadium compound ranges from 0.1 to 8.0 g/l.

4. Etching solution to any of the preceding claims, characterized in that the source for chlorate ions in the etching solution in process step A) is selected from sodium and potassium chlorate.

5. Etching solution according to any of the preceding claims, characterized in that the chlorate ion concentration ranges between 0.0016 and 0.1 2 mol/l.

6. Etching solution according to any of the preceding claims, characterized in that the sulphuric acid concentration ranges between 50 and 80 vol.%.

7. Etching solution according to any of the preceding claims, characterized in that the etching solution further comprises a second oxidizer in an amount of 2 to 20 g/l with the standard oxidising potential exceeding that of chlorate ions.

8. Etching solution according to claim 7, characterized in that the oxidizer is a periodate compound.

9. Etching solution according to any of the preceding claims, characterized in that the etching solution further comprises phosphoric acid in a concentration range between 1 0 and 40 vol.%.

10. Process for metallizing electrically nonconductive plastic surfaces of articles, comprising the process steps of:

A) etching the plastic surface with an etching solution according to any of the claims 1 to 9;

C) metallizing the plastic surface with a metallizing solution.

1 1 . Process according to claim 10, characterized in that the temperature during process step A) is kept between 20 and 65 °C.

12. Process according to claim 10, characterized in that the temperature during process step A) is kept between 40 and 65 °C.

13. Process according to claims 10 to 12, characterized in that the metal in process step

B) is palladium.

14. Process according to claims 10 to 13, characterized in that the plastic surface has been manufactured from at least one electrically nonconductive plastic and the at least one electrically nonconductive plastic is selected from the group comprising an acrylonitrile-butadiene-styrene copolymer, a polyamide, a polycarbonate and a mixture of an acrylonitrile-butadiene-styrene copolymer with at least one further polymer.

15. Process according to claims 10 to 14, characterized in that the following further process step is performed between process steps A) and B):

A i) treating the plastic surface in a solution comprising a reducing agent for chlorate ions.

16. Process according to claim 15, characterized in that the reducing agent is selected from the group consisting of hydroxylammonium sulphate, hydroxylammonium chloride and hydrogen peroxide.

17. Process according to claims 10 to 16, characterized in that the following further process step is performed between process steps A) and B):

A i) treating the plastic surface in a solution comprising a neutralizing agent comprising a source of hydroxide ions.

18. Process according to claims 10 to 17, characterized in that the following further process steps are performed between process steps B) and C):

B i) treating the plastic surface in an aqueous acidic solution and

B ii) electrolessly metallizing the plastic surface in a metallizing solution.