BR112014029353B1 - process for metallizing non-conductive plastic surfaces - Google Patents

Abstract

PROCESS FOR METALIZING NON-CONDUCTIVE PLASTIC SURFACES. The present invention relates to a process for metallizing non-conductive plastics using a hexavalent chromium free etching solution. The etching solution is based on a sulfuric acid solution containing a source of chlorate ions. After treating the plastics with the etching solution, the plastics are metallized using known processes.

Description

Field of Invention

[0001] The present invention relates to the pre-treatment of non-conductive plastic surfaces before their metallization and can be applied in various industries in which decorative or functional metallic coating of plastic parts is required. Pre-treatment is done in a hexavalent chromium free solution.

Background of the Invention

[0002] A conventional method of pre-treatment of non-conductive plastic surfaces before their metallization without current (electroless), mainly electroless coating with nickel or copper, consists of etching the surface in a solution containing hexavalent chromium, followed by by activation in an ionic or colloidal solution of palladium compounds and either reduction in sodium hypophosphite solution (in most cases) or acceleration in an acidic solution (usually hydrochloric acid) of palladium ions or colloidal particles of palladium, respectively, adsorbed onto the plastic surface.

[0003] Etching during the pretreatment step is required for hydrophilization purposes so that the surface becomes hydrophilic at other stages of the process in aqueous solutions, with sufficient amounts of adsorbed palladium salts, and to ensure binding from the metallic coating to the non-conductive plastic surface. Activation with subsequent reduction or acceleration is performed to initiate electroless deposition of the metal into the plastic. Then electroless coating with metal on the plating solution is performed by autocatalytic reaction in which the metal deposited on the surface acts as a catalyst for further deposition. Nickel and copper metals are the most used for this electroless coating.

[0004] Then electrolytic or galvanic coating can be performed on the first metallic layer. Various metals can be applied, for example, chromium, nickel, copper and brass or other alloys of the mentioned metals.

[0005] The main defects of the conventional method are related to the carcinogenicity of the chromic acid of the etching solution. In addition, metal deposited during the electroless deposition step, for example nickel, also covers insulated rack parts with plastisol, which results in metal losses from subsequent electrochemical metal coating solutions, and therefore is not desired

[0006] Several methods to overcome this problem have been suggested in the prior art.

[0007] US Patent Application No. 2005/0199587 A1 discloses a method of etching non-conductive plastic surfaces with an acidic solution containing 20-70 g/l potassium permanganate. The optimum concentration of KMnO4 in the above-mentioned method is about 50 g/l. When the concentration is below 20 g/l, the solution is ineffective, with the upper limit of concentration determined by the solubility of potassium permanganate. The etching is followed by activation in an amine-containing palladium salt solution and further reducing treatment, for example, in a borohydride, hypophosphite or hydrazine solution.

[0008] This method, however, has substantial shortcomings. With high concentrations of permanganate in the etching solution (approximately 50 g/l recommended, with phosphoric acid approximately 48% v/v), it decomposes very quickly, particularly at high temperatures. The recommended temperature is 37°C (ie 100°F). Tests have shown that at this temperature the solution becomes ineffective after 4 to 6 hours, that is, the plastic surface is not hydrophilic and remains uncoated in some places during metallization; in coated areas, adhesion to the plastic is very poor. It is often necessary to adjust the solution with new portions of permanganate, which is not profitable. In addition, insoluble permanganate decomposition products are formed, contaminating the surface being metallized;

[0009] In addition, etching in the permanganate solutions activates the plastisol insulation surface of the rack which is coated with the etching reaction product ie manganese dioxide. This stimulates the adsorption of palladium compounds on the plastisol, which tends to metallize in electroless plating solutions. Formation of manganese dioxide on surfaces is a characteristic of 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 metallization stage.

[0010] Lithuanian patent application number LT 2008-082 also deals with the pre-treatment of non-conductive plastic surfaces before metallization. A composition for pretreatment with etching eg polyimide for 1 - 2 minutes at a temperature of 10 - 80°C, 0.005 - 0.2M oxidizing solution in sulfuric acid with a concentration between 13 mol/L is disclosed. (about 75% by vol.) and 17 mol/L (about 90% by vol.), where the oxidants can be KMnO4, HCIO4, V2O5, KCIO3. In the case of a chlorate (ClO3-, M = 83.5 g/mol), this corresponds to a concentration between 0.4 and 16.7 g/l.

[0011] An example is provided in this application in Table 2 which contains 7 mol/L (about 50% by vol.) sulfuric acid and 0.2 mol/L (16.7 g/L) of chlorate. It has been found, however, that such high concentrations of chlorate result in rapid decomposition of the pretreatment solution, which is undesirable.

Description of the Invention

[0012] The present invention is therefore based on the problem that it has not been possible until now to carry out the metallization of articles made of electrically non-conductive plastic in an environmentally safe manner with sufficient process reliability and adhesion strength of the subsequently applied metallic layers .

[0013] It is, therefore, an objective of the present invention to find etching solutions for pretreatment of electrically non-conductive plastic surfaces of articles, which are non-toxic and provide sufficient adhesion strength of the metal layers applied on the plastic surface .

[0014] This objective is achieved using a strong water solution containing 0.2 to 15.0 g/l of soluble chlorate (based on KClO3, M = 122.55, ie, 0.0016 mol/l to 0, 12 mol/l) in 50-80% v/v sulfuric acid for the plastic surface etching in the application, as a method of treating the plastic surface before its electroless metallization, consisting of the plastic etching by means of an inorganic acid solution with an oxidant, activation by the palladium salt solution, and treatment by reducing or accelerating solution. The etching is preferably made at room temperature (15 - 28°C, preferably 20 - 25°C), but it can also be at higher temperatures of up to 40°C or 50°C as long as the stability of the solution be controlled. The pretreatment solution may optionally contain up to 20 g/l of another oxidant, with the standard oxidation potential exceeding that of chlorate.

[0015] The etching time varies with the material and shape of the substrate and can be determined by routine experiments. Generally it ranges between 1 and 20 minutes, preferably no more than 10 minutes.

[0016] The source of the chlorate ions can be any water-soluble salt. Chlorates most commonly used are sodium and potassium.

[0017] The concentration of chlorate ions in the etching solution is in the range between 0.0016 mol/l and 0.12 mol/l, or preferably up to 0.03 mol/l or even more preferably up to 0.04 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.

[0018] The concentration of sulfuric acid is between 50 and 80% by volume, preferably between 55 and 70% by volume and even more preferably between 60 and 65% by volume.

[0019] Optionally phosphoric acid, as an additional acid, can be included in the etching solution. The concentration of phosphoric acid typically ranges from 10 to 40% by volume, preferably between 15 and 25 or 30% by volume. When phosphoric acid is additionally used, the adhesion of the metallic layer can surprisingly be further increased.

[0020] A mixture of sulfuric acid between 60 and 65% by volume and phosphoric acid between 20 and 30% by volume is particularly preferred.

[0021] The method of pre-treatment of the surface of plastics before their electroless metallization, comprising the etching of the plastic in an inorganic acid solution with the addition of an oxidant, activation in a palladium salt solution, and treatment in reducing or accelerating solution, it is characterized by the etching of the plastic surface by the solution of 0.02 - 15.0 g/l of soluble chlorate (for example, 0.5 - 5 g/l soluble chlorate) in 50-80 % v/v sulfuric acid at room temperature and further treatment, prior to activation by means of the palladium compound solution and treatment with a reducing/accelerating solution in alkali metal hydroxide solution.

[0022] The etching solution may optionally contain 2 to 20 g/l of additional oxidizer, with the standard oxidizing potential exceeding that of the chlorate ions.

[0023] The alkali metal chlorate and sulfuric acid form a yellow compound, whose normal oxidizing potential in the H2SO4 solution is sufficient for reaction with the plastic surface at room temperature. Due to this reaction, the plastic surface becomes hydrophilic and adsorbs the palladium compound with sufficient intensity. The yellow colored product of the reaction between chlorate and sulfuric acid is a poison for the palladium catalyst. During etching, it penetrates the surface layers of the rack's plastisol insulation and prevents electroless metal deposition on the plastisol in electroless plating solutions; the metallization process being carried out on the non-conductive surface of the plastic is not affected.

[0024] With the dissolution of 1 to 2 g/l of sodium or potassium chlorate plus 5 to 10 g/l of a second strong oxidizer, for example, NaBiO3, the etching properties are maintained, at room temperature, for several days, and the solution can be used without adjustments. If only sodium/potassium chlorate is present in the solution, the etching properties remain for a much shorter period (up to 24 hours).

[0025] An important characteristic feature of the proposed method that makes it different from permanganate etching is that very high adhesion values between the coating and plastics are obtained, often exceeding 1.2 to 1.3 kg/cm) . These values depend, in addition to the composition of the etching solution and the etching time (there is an optimal etching time for each composition), on the composition of the activation solution. Typically, when real activation solutions are used the resulting adhesion values are greater than those obtained with colloidal activation solutions.

[0026] The etching solution can be prepared as follows:

[0027] 700 ml of concentrated sulfuric acid are mixed with 300 ml of deionized water. The solution is allowed to cool. Then 2 g of potassium chlorate plus 10 g of sodium perchlorate are dissolved in the solution. The solution is ready to use. The second oxidizing agent sodium perchlorate, which is stronger than potassium chloride, is optional. It extends the lifetime of the composition, but is not necessary for good adhesion of the subsequent metallic coating layer.

[0028] When the amount of water used for the preparation of the solution exceeds 50% by volume compared to sulfuric acid, no yellow plastic-oxidizing compound is formed between the chlorate ions and the sulfuric acid molecules; therefore, the water content of the solution preferably should not exceed 50% by volume.

[0029] When the amount of water used for the preparation of the solution is less than 20% by volume compared to sulfuric acid, the surface of plastics is decomposed during etching due to too high a concentration of sulfuric acid; therefore, no adhesion between the chemical nickel coating and the plastic is obtained.

[0030] If the amount of potassium chlorate dissolved in the solution is less than 0.5 g/l, the etching process takes more than 15 min; therefore, such concentration is not acceptable.

[0031] If the amount of potassium chlorate dissolved in the solution exceeds 5.0 g/l, super strong water can be observed after the minimum period of strong water, ie 2 to 3 minutes, which results in a force of much weaker adhesion, due to which this high concentration of chlorate is also not acceptable. However, depending on the substrate material, higher concentrations of up to 15 g/l may be acceptable resulting in sufficient adhesion.

[0032] The purpose of the present invention is achieved by the following process according to the invention:

[0033] Process to electrically metallize non-conductive plastic surfaces of articles, consisting of the process steps of: A) plastic surface etching with an etching solution as described above containing a source of chlorate ions resulting in a concentration from 0.0016 to 0.12 mol/l of chlorate ions in 50-80% v/v sulfuric acid; B) treatment of the plastic surface with a solution of metal colloid or a metal compound, 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) metallization of plastic surface with a plating solution;

[0034] Articles in the context of this invention are understood as articles which have been manufactured from at least one electrically non-conductive plastic or which have been covered with at least one layer of at least one electrically non-conductive plastic. The articles thus have surfaces of at least one electrically non-conductive plastic. Plastic surfaces are understood in the context of this invention to mean those surfaces of articles.

[0035] The process steps of the present invention are carried out in the specified sequence, but not necessarily in immediate succession. It is possible that further process steps and additionally washing steps in each case, preferably with water, are carried out between the steps.

[0036] Plastic surfaces have been fabricated from at least one electrically non-conductive plastic. In one embodiment of the present invention, the at least one electrically non-conductive plastic is selected from the group consisting of an acrylonitrile-butadiene-styrene copolymer (ABS copolymer), a polyamide (PA), a polycarbonate (PC) and a blend of a ABS copolymer with at least one other polymer.

[0037] In a preferred embodiment of the invention, the electrically non-conductive plastic is an ABS copolymer or a mixture of an ABS copolymer with at least one other polymer. The at least one other polymer is more preferably polycarbonate (PC), which means that particular preference is given to ABS/PC blends.

[0038] The etching solution of the invention preferably does not contain any chromium or chromium compounds; the etching solution does not contain chromium(III) ions or chromium(VI) ions. The etching solution of the invention is thus free of chromium or chromium compounds; the etching solution is free of chromium(III) ions and chromium(VI) ions.

[0039] In another preferred embodiment of the invention, the following additional process step is performed between process steps A) and B): A i) treating the plastic surface in a solution containing an alkaline solution.

[0040] The additional process step A i) is also referred to as neutralization treatment. Any source of alkanility can be used, with an aqueous solution of sodium hydroxide being preferred.

[0041] In another alternative embodiment of the invention, the following additional process step is performed between process steps A) and B): A i) treating the plastic surface with a solution containing a reducing agent for chlorate ions and optionally a second oxidizing agent.

[0042] The additional process step A i) is also referred to as reduction treatment. This reduction treatment reduces chlorate ions and optionally a second oxidizing agent adhering to plastic surfaces and facilitates removal of these ions. The reducing agent is, for example, selected from the group containing hydroxylammonium sulphate, hydroxylammonium chloride and hydrogen peroxide.

[0043] The process of the present invention further comprises a process step B), in which the plastic surface is treated with a solution of a metal colloid or a metal compound.

[0044] The metal of the metal colloid or metal compound is selected from the group consisting of the transition group I metals of the Periodic Table of the Elements (TPE) and the transition group VIII of the TPE.

The transition metal group VIII of TPE is selected from the group containing palladium, platinum, iridium, rhodium and a mixture of two or more of these metals. The transition metal group I of TPE is selected from the group containing gold, silver and a mixture of these metals.

[0046] A preferred metal in metallic colloid is palladium. Metal colloid is stabilized with protective colloid. The protective colloid is selected from the group containing protective metallic colloids, protective organic colloids and other protective colloids. As a protective metallic colloid, tin ions are preferred. The protective organic colloid is selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone and gelatin, preferably polyvinyl alcohol.

[0047] In a preferred embodiment of the invention the metal colloid solution in process step B) is an activating solution with a palladium/tin colloid. This colloidal solution is obtained from a palladium salt, a tin(II) salt and an inorganic acid. A preferred palladium salt is palladium chloride. A preferred tin(II) salt is tin(II) chloride. The inorganic acid can be hydrochloric acid or sulfuric acid, preferably hydrochloric acid. The colloidal solution is formed by reducing palladium chloride to palladium with the help of tin(II) chloride. Conversion of palladium chloride to colloid is complete; therefore, the colloidal solution no longer contains any palladium chloride. The palladium concentration 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 tin(II) chloride concentration 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 hydrochloric acid concentration is 100 ml/l - 300 ml/l (37% by weight of HCl). The palladium/tin colloidal solution additionally contains tin(IV) ions formed by oxidation of tin(II) ions. The temperature of the colloidal solution during step B) of the process 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.

[0048] In another embodiment of the invention, in step B of the process, solution of a metallic compound is used in place of the metallic colloid. The metal compound solution used is a solution containing an acid and a metal salt. The metal in the metal salt consists of one or more of the TPE transition group I and VIII metals listed above. The metal salt may be a palladium salt, preferably palladium chloride, palladium sulfate or palladium acetate, or a silver salt, preferably silver acetate. The acid is preferably hydrochloric acid. Alternatively, it is also possible to employ a complex metal salt, for example a palladium complex salt, such as a palladium-aminopyridine complex salt. The metal compound in process step B) is present at a concentration of 40 mg/l to 80 mg/l, based on the metal. The metal compound solution can be employed at a temperature of 25°C to 70°C, preferably at 25°C. The treatment time with the metal compound solution is 0.5 min - 10 min, preferably 2 min - 6 min and more preferably 3 min - 5 min.

[0049] Between process steps A) and B), the following additional process step can be performed: A ii) treat the plastic surface in an acidic aqueous solution.

[0050] Preference is given to the execution of process step A ii) between process steps A i) and B). If, in the process according to the invention, process step A i) is followed by protecting the racks, process step A ii) is more preferably carried out between protecting the racks and process step B).

[0051] The treatment of plastic surfaces in process step A ii) is also referred to as preceding dipping, and the acidic aqueous solution used as a preceding dipping solution. The preceding dip solution has the same composition as the colloidal solution from process step B), without the presence of the metal in the colloid and its protective colloid. The previous dip solution, in the case of using a colloidal palladium/tin solution in process step B), contains only hydrochloric acid if the colloidal solution also contains hydrochloric acid. For preceding immersion, brief immersion in the preceding immersion solution at room temperature is sufficient. Without rinsing the plastic surfaces, they are additionally treated directly with the colloidal solution from process step B) after the treatment with the preceding dip solution.

[0052] Process step A ii) is preferably performed when process step B) involves treating the plastic surface with a solution of a metal colloid. Process step A ii) can also be carried out when process step B) involves treating the plastic surface with a metal compound solution.

[0053] After treating the plastic surfaces with the metal colloid or metal compound from process step B), they can be rinsed. In another embodiment of the invention, the following additional process steps are carried out between process steps B) and C): B i) treatment of the plastic surface with an acidic aqueous solution and B ii) electroless metallization of the plastic surface in a solution of metallization.

Tabela 1: Modalidade de metalização de plástico min[0054] The modality is shown schematically in Table 1.

Table 1: Plastic plating modality min

[0055] These additional process steps B i) and B ii) are employed when articles are to be metallized by an electroless metallization process, i.e., a first layer of metal is to be applied to the plastic surfaces by an electroless process.

[0056] If the activation in process step B) was performed with a metal colloid, the plastic surfaces are treated in process step B i) with an accelerator solution to remove colloid constituents in the colloid solution, for example a colloid protective, of plastic surfaces. If the colloid of the colloid solution from 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 consisting of sulfuric acid, hydrochloric acid, citric acid and tetrafluoroboric acid. In the case of a palladium/tin colloid, the accelerator solution helps remove the tin compounds that served as the protective colloid.

[0057] Alternatively, in process step B i), a reducing treatment is performed when, in process step B), a solution of a metal compound was used in place of a metal colloid for activation. The reductant solution used for this purpose then includes whether 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(II) chloride. The reducing solution may also contain another reducing agent such as NaH2PO2 or a borane or borohydride such as an alkali metal borane or alkaline earth metal borane or dimethylaminoborane. Preference is given to using NaH2PO2 in the reducer solution.

[0058] After acceleration or treatment with the reducer solution in process step B i), the plastic surfaces can first be washed.

[0059] Process step B i) and optionally one or more washing steps are followed by process step B ii) in which the plastic surfaces are metallized by the electroless process. Electroless nickel plating is carried out, for example, using a conventional nickel bath that includes, among others, nickel sulphate, a hypophosphite, for example, sodium hypophosphite, as a reducing agent, and also organic complexing agents and pH adjusters ( for example a tampon). The reducing agent used can also be dimethylaminoborane or a mixture of hypophosphite and dimethylaminoborane.

[0060] Alternatively, it is possible to use an electroless copper bath for electroless coating with copper, the copper bath typically containing a copper salt, for example, copper sulfate or copper hypophosphite, in addition to a reducing agent such as formaldehyde or a hypophosphite salt, for example an alkali metal salt 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.

[0061] The surface, thus made conductive, can subsequently be electrolytically additionally metallized to obtain a functional or decorative surface.

[0062] 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 carried out 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. These deposition baths are familiar to those skilled in the art. A Watts nickel bath is typically used as a shiny nickel bath, this one containing nickel sulfate, nickel chloride and boric acid, in addition to saccharin as an additive. An example of a composition used as a bright copper bath is one containing copper sulphate, sulfuric acid, sodium chloride and organic sulfur compounds where the sulfur is in a low oxidation state, eg organic sulphides or disulfides as additives .

[0063] 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 metals listed above for the deposition baths.

[0064] In another embodiment of the invention, after the process step C), the following additional process step is performed: C i) storage of the metallized plastic surface at high temperature.

[0065] As in all electroplating processes in which a non-conductor is coated with metal in a wet chemical process (wet-chemical means), the adhesion force between the metal and the plastic substrate increases in the first period after the application of the metallic 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 completed after about an hour at 80°C. It is assumed that the initially low adhesion strength is caused by a thin layer of water that lies on the boundary between the metal and the non-conductive substrate and prevents the formation of electrostatic forces.

[0066] The process according to the invention thus allows, with good process reliability and excellent adhesion strength of the subsequently applied metallic layers, obtaining metallization of electrically non-conductive plastic surfaces of articles. The adhesion strength of metallic layers applied to plastic surfaces reaches values up to 2.7 N/mm (corresponding to approximately 2.7 kg/cm, 1 kg/cm = 0.98 N/mm) or more. Thus, the adhesion strengths obtained are also above those obtainable according to the prior art after etching plastic surfaces using chromosulphuric acid (see Examples 2 and 3).

[0067] In general, adhesion values of more than 0.8 N/mm are required for industrial applications and objects are plated in a non-complex way. In general, the greater the adhesion, the better the deposit stability.

[0068] Furthermore, not only flat plastic surfaces are metallized with high adhesion strength by the process according to the invention; on the contrary, for example, showers are also provided with a homogeneous and strongly adhered metallic coating.

[0069] The treatment of plastic surfaces by the process according to the invention is preferably carried out in a conventional immersion process, successively immersing the articles in solutions in vessels, in which the respective treatment occurs. In this case, the items can be immersed in the solutions or fixed to racks or accommodated in drums. Attachment to racks is preferred. Alternatively, the articles can also be treated in what are called conveyor plants, placed, for example, on trays and being transported continuously through the plants in a horizontal direction.

Examples of Work

[0070] The working examples described below are intended to illustrate the invention in detail.

Example 1

[0071] ABS (acrylonitrile-butadiene-styrene copolymer) and PC/ABS (a blend of 45% polycarbonate and 55% acrylonitrile butadiene styrene copolymer) are acid etched, according to US Patent Application No. 2005/0199587 A1: in a 45% v/v phosphoric acid solution containing 50 g/l of KMnO4 at 37°C for 5 min (for ABS) or 15 min (for PC/ABS), or in a solution of 50 to 80% v/v sulfuric acid with 0.5 to 5.0 g/l KClO3 being added oxidant at 20°C for 1 to 12 min. When using etching, the plastics are immersed for 1 to 2 min in a neutralizing solution at room temperature containing 10 g/l of NaOH, followed by activation of the real (5 min at 20°C) or colloidal solution (2 min at 35°C) of palladium compounds (colloidal solution is proprietary solution of DOW Chemical Company (“DOW”)). The concentration of PdCl2 in the real solution is 0.1 g/l, the pH of the solution is 2.7. Upon activation of the real Pd solution, the plastics are kept for 5 min. in a solution containing 20 g/l of sodium hypophosphite, pH 9, at 60°C. Upon activation in the proprietary colloidal solution, the plastics are treated for 2 min. at 40°C with DOW's proprietary accelerator solution. Thereafter, the plastics are nickel coated using Dow's Niposit-PM nickel plating process. The coating quality is evaluated based on factors such as the plastic surface completely/not completely coated, the insulated rack with coated or uncoated plastisol, and the adhesion strength of electroless nickel to plastic. To assess adhesion, the Ni coating is thickened in a bath of galvanic copper and the force required to peel a 1 cm wide strip of plastic is measured (kg/cm). For ABS parts under test, the etching time in the permanganate solution was 5 min, for PC/ABS parts under test it was 15 min. The etching time in the chlorate solution was 5 min. for all parts. The pretreatment conditions of plastics for metallization and the results of metallization (electroless nickel plating) are shown in Table 2 below. Table 2

[0072] Test pieces 1 to 4 show that in the case of permanganate-based etching, the plastisol insulation of the rack is partially coated with electroless nickel, whereas in the case of chlorate-based etching the insulation remains clean . Furthermore, the adhesion values between the Ni and ABS coating are considerably higher in the case of chlorate etching for both ionic and colloidal activation solutions.

[0073] The same results are observed in the case of the PC/ABS electroless nickel coating (Test pieces 5 to 8): In the chlorate etching process, the plastisol insulation is not coated at all, and the adhesion values are considerably higher, in particular when ionic activation solution is used.

[0074] When the concentration of KCIO3 in the etching solution is less than 0.5 g/l, ABS is not coated with electroless nickel or is incompletely coated (Test piece 9). When the KClO3 concentration is greater than 5 g/l (Test piece 10), super strong water occurs after 5 min of strong water; therefore the adhesion value of the coating is considerably lower (not enough for practical applications). When the recommended KClO3 concentration values are exceeded, analogous results are also obtained for PC/ABS metallization (Test Pieces 11 and 12).

[0075] In the case where the concentration of H2SO4 in the etching solution is less than 50% v/v, the etching agent is not sufficiently effective; therefore, the plastic is not electroless nickel coated at all or is incompletely coated (Test piece 13). When the concentration of H2SO4 is greater than 80% v/v (Test piece 14), the plastic's super strong water occurs and the adhesion between the chemical nickel coating and the plastic is insufficient.

Example 2

[0076] A round ABS plastic substrate disc (Novodur P2MC, from Ineos) having a diameter of 7 cm was attached to a stainless steel wire. The substrate was then dipped into various pretreatment etching solutions according to the invention as specified in Table 4 for 4 minutes at a temperature of 22°C (process sequence is shown in Table 3). Subsequently, the substrate was washed under running water for about one minute. After subsequent washing, neutralization (process step A i)) and brief immersion in a 300 ml/l solution of 36% hydrochloric acid (process step A ii)), the substrate was activated in a colloidal activator based on a palladium colloid (Atotech's Adhemax Aktivator NA, 100 ppm palladium) at 40°C for three minutes (process step B)).

Tabela 4: Forças de adesão de uma camada de cobre/níquel em várias misturas de ABS de acordo com o Exemplo 2

[0077] After subsequent washing, the protective shells of the palladium particles were removed at 40°C for three minutes (Atotech Adhemax ACC1 accelerator, process step B i)). The substrate was subsequently coated with nickel at 45°C without external current for ten minutes (Adhemax LFS, from Atotech, process step B ii)), washed and coated with copper at 3.5 A/dm2 at room temperature for 70 minutes (Cupracid HT, from Atotech, process step C)). After washing, the panel was stored at 70°C for 60 minutes (process step C i)). Subsequently, a knife was used to cut a strip of metallized plastic substrate about 1 cm wide, and a tensile tester (from Instron) was used to pull the metallic layer out of the plastic (ASTM B 533 1985 Reapproved 2009). Adhesion strengths shown in Table 4 were obtained. Table 3: Sequence of Process Steps from Example 2

Table 4: Adhesion strengths of a copper/nickel layer on various ABS blends according to Example 2

[0078] From Table 4 it becomes apparent that with careful selection of the concentration of chlorate in combination with sulfuric acid, very high adhesion values can be obtained. Test piece number one shows that concentrations as low as 0.2 g/l of potassium chlorate (corresponding to a ClO3- concentration of 0.0016 mol/l) are sufficient to obtain good adhesion. Maximum values are obtained in a range of about 1.5 g/l of potassium chlorate. After that, a decline in adhesion strength can be observed. It is noted that compositions including a mixture of sulfuric acid and phosphoric acid (Table 4, Part Nos. 9 to 16) generally show higher adhesion values at the same concentration of chlorate ions compared to etching in solutions containing only sulfuric acid and are thus particularly preferred.

Claims (15)

1. A process for metallising plastic surfaces of non-electrically conductive articles comprising the steps of: A) attacking the plastic surface with an aqueous etching solution; B) treating the plastic surface with a solution of a metal colloid or a metal compound, the metal being selected from the metals of transition group I of the Periodic Table of Elements and transition group VIII of the Periodic Table of the Elements, and C) metallizing the plastic surface with a metallizing solution; characterized by the fact that the etching solution includes a source of chlorate ions resulting in a concentration of 0.0016 to 0.12 mol/l of chlorate ions and 50-80% v/v of sulfuric acid. chromium ion-free etching solution VI. 2. Process according to claim 1, characterized in that the source of chlorate ions in the etching solution of process step A) is selected between sodium chlorate and potassium chlorate. 3. Process according to claim 1 or 2, characterized by the fact that the concentration of chlorate ions is in the range between 0.003 and 0.08 mol/l. 4. Process according to claims 1 or 2, characterized by the fact that the concentration of chlorate ions is in the range between 0.01 and 0.06 mol/l. 5. Process according to claims 1 or 2, characterized in that the concentration of chlorate ions is in the range between 0.004 and 0.04 mol/l. 6. Process according to any one of claims 1 to 5, characterized in that the concentration of sulfuric acid ions is in the range between 60 and 70% by volume. 7. Process according to any one of claims 1 to 6, characterized in that the etching solution additionally includes a second oxidizing agent in an amount of 2 to 20 g/l with the standard oxidizing potential exceeding that of ions of chlorate. 8. Process according to any one of claims 1 to 7, characterized in that the etching solution additionally includes phosphoric acid. 9. Process according to claim 8, characterized in that the concentration of phosphoric acid is in the range between 10 and 30% by vol. 10. Process according to any one of claims 1 to 9, characterized in that the metal in process step B) is palladium. 11. Process according to any one of claims 1 to 10, characterized in that the plastic surface was manufactured from at least one electrically non-conductive plastic, and the at least one electrically non-conductive plastic is selected from the group consisting of an acrylonitrile-butadiene-styrene copolymer, a polyamide, a polycarbonate and a blend of an acrylonitrile-butadiene-styrene copolymer with at least one other polymer. 12. Process according to any one of claims 1 to 11, characterized in that the following additional process step is carried out between process steps A) and B): A i) treatment of the plastic surface in a solution containing an agent reducer for chlorate ions. 13. Process according to claim 12, characterized in that the reducing agent is selected from the group consisting of hydroxylammonium sulfate, hydroxylammonium chloride, and hydrogen peroxide. 14. Process according to any one of claims 1 to 13, characterized in that the following additional step of the process is carried out between process steps A) and B): A i) treatment of the plastic surface in a solution containing an agent a neutralizing agent that includes a source of hydroxide ions. 15. Process according to any one of claims 1 to 14, characterized in that the following additional process steps are carried out between process steps B) and C): B i) treatment of the plastic surface in an acidic aqueous solution and B ii) electroless metallization of the plastic surface in a metallization solution.