EP0131195B1 - Process for the activation of substrates for electroless metal plating - Google Patents

Description

The invention relates to a gentle method for activating non-conductive or semiconductive substrate surfaces for chemogalvanic metal deposition by means of solutions or dispersions of complex compounds of elements of the 1st and 8th subgroups of the periodic table.

Such methods have been described many times in the literature.

For example, in AT-B 286 058 it is proposed that complex compounds include those of amines, amides, carboxylic acids, ketones, olefins and others. to use.

From DE-A 3 025 307 it is also known to carry out the activation by means of complexes of nitriles, diketones and dienes.

According to DE-A 2 116 389, complexes of N-containing compounds, for. B. pyridine derivatives, recommended.

Although excellent activation effects are sometimes achieved with these processes even on uneven and acid- or alkali-sensitive substrates, they all have the serious disadvantage that the metal complex solutions used are not sufficiently stable in storage.

This also applies to the process according to DE-A 2 451 217, in which solutions of a palladium-O complex of polyunsaturated ketones are used for the activation, which additionally stabilize the system as phosphites as n-donors and as olefinically or acetylenically unsaturated compounds as n acceptors included. However, the addition of these additional complexing agents lowers the catalytic effect of the metal complexes, so that the substrates to be activated have to be subjected to extensive thermal aftertreatment. In addition, the palladium-O complexes mentioned have the disadvantage that they only partially very toxic aromatics and not sufficiently soluble in the other common solvents such as 1,1-dichloroethane, trichlorethylene, ethanol and cyclohexane.

Finally, all the gentle activation methods have in common that they work with the volatile solvents mentioned above, which results in a constant change in the concentration of the activation baths.

So it is understandable that the activation baths need constant, careful monitoring. They have to be supplemented with solvents and / or concentrate in order to ensure a constant production process.

The object of the present invention was therefore to develop activators which are stable in storage and whose continuous monitoring is possible with simple physical and / or chemical methods.

verwendet, worin unabhängig voneinander R, und R₄ einen gegebenenfalls substituierten Alkyl-, Cycloalkyl-oder Arylrest und R₂ und R₃ Wasserstoff oder Alkyl bedeuten.This object is achieved in that complex compounds of the elements of the 1st and 8th subgroup of the periodic table in the oxidation states 1-4 with unsaturated ketones of the formula

used, wherein independently of one another R, and R _{4 are} an optionally substituted alkyl, cycloalkyl or aryl radical and R ₂ and R _{3 are} hydrogen or alkyl.

The complexes of the compounds of the formula are notable for good solubility in all organic solvents customary in the industry. They can be used in concentration ranges from 0.001 g / I up to the respective solubility limit. It is preferable to work with 0.1-3.0 g / l of these substances.

Thanks to their high storage stability (no clouding of the solutions - sometimes after weeks of storage) and their strong sorption in the ultraviolet and / or visible spectral range, they are ideal for the continuous concentration monitoring of your solutions with a photometer.

Otherwise, the sorption properties of the complex compounds to be used according to the invention can be increased further by introducing special substituents (in particular NO ₂ and CN) into the radicals R _i and R ₄ .

The influence of electron-withdrawing or electron-donating substituents on the light absorption properties of carbon molecules is known and can be seen, for example, from D.H. Williams and J. Flemming, "Spectroscopic methods in organic chemistry", Georg Thieme Verlag Stuttgart (1971).

The complexes of the compounds of the formula are partly known or obtainable by methods known per se (cf. Parshal and Wilkinson, "Inorganic Chemistry" 1, (1962), p. 896) by, for. B. a suitable aqueous solution of the noble metal salt to an excess compound of formula I and at temperatures of 20-150 ° C preferably 60-120 ° C, the complex formation leads to the end.

After cooling, the complex separates out in solid form. It is washed, dried, optionally recrystallized and dissolved in a suitable solvent.

Suitable metals for the preparation of the complexes are e.g. B. Pd, Pt, Ag and Au, of which the palladium in the oxidation states 1 and 2 is particularly preferred.

Suitable compounds of the formula are, above all, those in which "alkyl" stands for C, -C _2o-alkyl radicals, "cycloalkyl" for cyclohexyl and "aryl" for benzene radicals, the alkyl radicals being represented by Cl, CN, N0 ₂ , C _l -C ₄ alkoxy or C ₁ -C ₄ alkoxy-C ₁ -C ₄ alkoxy, the cycloalkyl radicals by CH ₃ and the aryl radicals by Cl, N0 ₂ , C _l -C ₄ - Alkyl or C, -C ₄ alkoxy may be substituted.

Complexes to be used with particular preference are derived from compounds of the formula in which

R ₁ and R _{4 are} C ₁ -C ₂₀ alkyl, preferably C ₁ -C ₆ alkyl, R ₂ and R _{3 are} hydrogen or C, -C ₄ alkyl, preferably methyl.

Examples include: mesityl oxide, n-buten-3-one-2, n-hepten-3-one-2, n-hexen-3-one-2, n-decen-4-one-3,5-chloro penten-3-one-2, ethyl vinyl ketone, 3-methyl-octen-5-one-4, 3-methyl-penten-3-one-2, 7-methoxy-hepten-3-one-2 and cyclohexen-2- on.

In practice, the new activation process is generally carried out by wetting the substrate surfaces to be metallized with a dispersion or - preferably - a solution of the metal complex in a suitable organic solvent, removing the solvent and, if appropriate, sensitizing it with a suitable reducing agent. The substrate pretreated in this way can then be metallized in a conventional metallization bath.

In addition to the above-mentioned perchlorethylene, acetone, methanol, butanol and dimethylformamide, suitable solvents are also suitable.

Suitable reducing agents for the sensitization are aminoboranes, alkali hypophosphites and alkali borohydrides.

The substrates can be wetted by spraying, printing, impregnation or impregnation.

In order to increase the adhesion of the metal coating to the carrier surface, those solvents or solvent mixtures which lead to dissolution or swelling of the plastic surface to be metallized are particularly preferably used to carry out the method according to the invention.

The solvents are removed from the wetted substrates simply by evaporation or, in the case of higher-boiling compounds, by extraction.

According to a preferred method variant, the activation baths are monitored with a photometer as a detector. The wavelength of the filter should correspond to the absorption maxima of the solution. The measurement signal is recorded by a compensation recorder and called up by a clock generator at intervals of 0.1 seconds to several minutes. With the help of a computer, the missing components (solvent, activator) can be added.

A very particularly preferred embodiment of the method according to the invention consists in that the reduction in the metallization bath is carried out immediately with the reducing agent of the electroless metallization. This embodiment is particularly suitable for nickel baths containing amine borane or copper baths or silver baths containing formalin.

Metallization baths which can be used in the processes according to the invention are preferably baths with Ni, Co, Cu, Au, Ag salts or their mixtures with one another or with iron salts. Such baths are known in the art of electroless metallization of plastics.

Suitable substrates for the process according to the invention are: steels, titanium, glass, aluminum, textiles and flat structures based on natural and / or synthetic polymers, ceramics, carbon, paper, thermoplastics such as polyamide types, ABS (acrylonitrile butadiene styrene) polymers, polycarbonates, Polypropylene, polyester, polyethylene, polyhydantoin and thermosets such as epoxy resins, melamine resins, and their mixtures or copolymers.

• - Die eingesetzten Verbindungen zur Aktivierung von Substratoberflächen dürfen nicht zu einer irreversiblen Zerstörung des Metallisierungsbades führen.
• - Die lichtabsorptionsfähigen Substituenten dürfen nicht eine Fixierung der Aktivatoren an die Substratoberfläche verhindern.
• - Die lichtabsorptionsfähigen Substituenten dürfen nicht eine Komplexierung des Trägermolekuls mit den Elementen der 1. und 8. Nebengruppe verhindern.
• - Die besagten Elemente dürften mit a,ß-ungesättigten Verbindungen keine so starke Wechselwirkung eingehen, daß sie eine Katalyse zur chemischen Metallabscheidung verhindern.
• - Die verwendeten Lösungsmittel dürfen nicht im Absorptionsbereich des Aktivators Eigenabsorption aufweisen, müssen leicht entfernbar sein und dürfen nicht zu einem chemischen Abbau der metallorganischen Verbindung sowie zum völligen Auflösen der Substrate führen.
• - Um eine ausreichende Aktivierung zu erzielen, soll die Aktivierungszeit von einigen Sekunden bis zu einigen Minuten betragen.

Without restricting the scope of the method according to the invention, it is advisable to observe the following parameters when carrying out the method:

• - The connections used to activate substrate surfaces must not lead to irreversible destruction of the metallization bath.
• - The light-absorbing substituents must not prevent the activators from being fixed to the substrate surface.
• - The light-absorbing substituents must not prevent complexation of the carrier molecule with the elements of subgroups 1 and 8.
• - The said elements should not interact so strongly with α, β-unsaturated compounds that they prevent catalysis for chemical metal deposition.
• - The solvents used must not be self-absorbing in the absorption area of the activator, must be easily removable and must not lead to chemical degradation of the organometallic compound and complete dissolution of the substrates.
• - To achieve sufficient activation, the activation time should be from a few seconds to a few minutes.

example 1

A 20 x 20 cm square of a 0.2 mm thick polyester film (100% polyethylene terephthalate) is at room temperature for 30 seconds in an activation bath, which is made from 0.6 g according to Parshal and Wilkinson (see page 2), mesityl oxide-palladium chloride complex and 1 technical trichlorethylene is prepared, activated, dried at room temperature and then for 15 minutes in an aqueous alkaline nickel plating bath, which in 1 l 30 g NiS0 ₄ . 6H ₂ 0 11.5 g of citric acid, 18 ml of 2N DMAB (dimethylamine borane) solution, 2 g of boric acid and adjusted to pH 8.5 with 25% ammonia solution, electroless nickel-plated. After about 45 seconds the polymer surface begins to turn gray and after about 12 minutes the specimen is covered with a shiny - 0.15 µm thick nickel layer.

Example 2

A 140 x 250 mm injection-molded ABS plate (acrylonitrile-butadiene-styrene graft copolymer from Bayer AG) is activated in a solution of 500 ml of technical methanol, 50 ml of technical trichloroethene and 0.4 g of mesityl oxide-palladium complex for 5 minutes at room temperature , dried at RT, sensitized for 3 minutes in a reduction bath of 500 ml of ethanol and 50 ml of 2N DMAB solution and then nickel-plated at 33 ° C. in a conventional metallization bath from Blasberg GmbH and KG, 5650 Solingen. The test specimen is covered with a very fine nickel coating after only 4 minutes. After approximately 17 minutes, the chemical nickel layer has an average thickness of approximately 0.20 µm. After the test specimen is removed from the chemical metallization bath and rinsed with distilled water, it is switched as the cathode in a conventional acidic galvanic copper plating bath and is amplified to a thickness of approx. 40 ₁ 1m at 1.1 A / dm ² .

Example 3

A 150x200 mm injection molded polyethylene terephthalate plate is activated at room temperature for 30 seconds in an activation bath which is made up of 0.4 g mesityl oxide platinum complex and 650 ml tetrachlorethylene, dried at RT and then nickel-plated according to Example 1. You get a shiny metallic polymer plate with a - 0.15 ₁ 1m thick electrically conductive nickel coating.

Example 4

A 150 × 300 mm rectangle of a cotton fabric is immersed for 30 seconds in a solution of 0.5 g of mesityl oxide palladium chloride in 600 ml of methylene chloride, dried at room temperature and then nickel-plated in a reductive nickel bath according to Example 1 for 22 minutes.

After about 30 seconds the surface begins to turn dark and after 5 minutes a shiny metallic layer has been deposited.

Example 5

A 120x120 mm square of a conventional polyester-cotton blend is activated for 20 seconds in accordance with Example 1, sensitized in a reduction bath in accordance with Example 2, rinsed with distilled water and then coppered in a chemical copper bath from Schering AG, Berlin (West) for 20 minutes . A well-adhering, electrically conductive copper layer was deposited after only 5 minutes.

Example 6

An ABS plate is activated at RT for 5 min in a bath which is prepared from 500 ml of ethanol, 25 ml of 2,4-pentanedione and 0.4 g of n-3-hepten-2-one-palladium chloride, at 35 ° C. Dried for 5 minutes and then nickel-plated according to Example 1 over a period of 20 minutes. After galvanic reinforcement, the pull-off force of the metal layer is higher than the tensile strength of the metal layer.

Example 7

A polyamide 6,6 plate is activated according to example 6 in an activation bath which is adjusted to pH 2.5 with concentrated hydrochloric acid, washed with distilled water and then sensitized according to example 2 and then metallized for 20 minutes. A shiny metallic sample with an adherent metal coating is obtained.

Example 8

A 100x200 mm rectangle of a 2 mm thick with through holes, glass fiber reinforced epoxy resin plate laminated on both sides, is immersed in 1 I CH ₂ C1 ₂ in air in an activation bath of 0.5 g n-3-hepten-2-one-palladium chloride dried, sensitized according to Example 2 and then copper-coated according to Example 5 for 25 minutes. You get a plate through-plated with an electrically conductive Cu layer, which can be used for the production of electrical circuit boards.

The heptenone complex is made as follows.

6 g of aqueous Na ₂ PdC1 ₄ solution, which contains 15% by weight of Pd, 20 g of freshly distilled n-3-hepten-2-one are added dropwise at 110 ° C. in 15 minutes, the mixture is stirred for 25 minutes at the above temperature, then cooled to 0 ° C. After two hours, the yellow precipitate is filtered off with suction, washed 3 times with 75 ml of distilled water and then 2 times with 50 ml of cold ethanol after cleaning, dried, recrystallized from toluene / trichlorethylene (1: 1), dried in a drying cabinet under vacuum overnight . A pink-yellow crystalline solid with a decomposition point of 188 ° C. is obtained in 92% yield.

C: CI: Pd: O = 39.9: 14.1: 42.5: 6.6 (determined) C: CI: Pd: O = 33.1: 14.0: 41.9: 6.3 ( theoretically)

Claims (10)

1. Process for the activation of substrate surfaces for electroless metallisation by means of solutions or dispersions of complex compounds of elements of sub-groups 1 and 8 of the periodic table, characterised in that complex compounds of these elements in oxidation stages 1-4 with unsaturated ketones of the formula

wherein, independently of one another,

R₁ and R₄ denote an optionally substituted alkyl, cycloalkyl or aryl radical and

R₂ and R₃ denote hydrogen or alkyl, are used.

2. Process according to Claim 1, characterised in that complex compounds of Pd, Pt, Ag or Au are used.

3. Process according to Claim 1, characterised in that complex compounds based on ketones of the formula given in Claim 1, wherein

R, and R₄ denote C₁-C₆-alkyl and

R₂ and R₃ denote H or C₁-C₄-alkyl, are used.

4. Process according to Claim 1, characterised in that the solutions or dispersions are used without additional complexing agents of the series of donors and n-acceptors.

5. Process according to Claim 1, characterised in that the complex compounds are used in concentrations of 0.1 - 3.0 g/litre of solvent

6. Process according to Claim 1, characterised in that the activated substrates are introduced into wet chemical metallising baths, especially Cu, Ni, Co, Ag and Au baths.

7. Process according to Claim 1, characterised in that the concentration of the complex solutions in the activation baths is monitored continuously with a photometer.

8. Process according to Claim 1, characterised in that the palladium complex of n-but-3-en-2-one is used.

9.. The palladium complex of n-hept-3-en-2-one.

10. Use of the complex compound according to Claim 9 for the activation of substrates to be metallised.