EP0081129B1 - Method of activating substrate surfaces for electroless metal plating - Google Patents

Description

The invention relates to a method for activating substrate surfaces for the purpose of chemical metallization.

It is known that polymeric materials must be pretreated before chemical and subsequent galvanic metallization, R. Weiner Kunststoff-Gaivanisierung, Eugen G. Leuze Verlag, Saulgau / Württ. (1973). This is essentially the etching of the polymer surface e.g. with chromic sulfuric acid, the single and multiple rinsing with water, the detoxification with dilute sodium bisulfite solution, the further rinsing with water and the treatment of the substrate surface with a suitable activation bath, for example a palladium salt solution or a palladium sol.

During the etching, the polymer surface is changed so that caverns and vacuoles are formed. This is only possible with certain polymers e.g. in the case of 2-phase multicomponent graft or copolymers, such as ABS polymers, impact-resistant polystyrene or 2-phase homopolymers, such as partially crystalline polypropylene.

Furthermore, working with chromosulfuric acid or other oxidants is associated with a deterioration in the physical properties, such as notched impact strength, electrical surface resistance of the polymeric base material.

In addition, the hexavalent chromium introduced into the activation and metallization bath leads to poisoning of the baths.

The same disadvantages arise in processes in which the polymer surfaces are chemically changed by means of a strong gaseous oxidizing agent, for example hot SO ₃ vapor.

So that the ionic palladium fixed to the substrate surface enables a catalytic reduction of the metal ion in the chemical metallization bath, it must be reduced to the metal. The ionogenic palladium is reduced either in an acidic tin (II) chloride bath or by introducing tin (II) chloride into a strong hydrochloric acid palladium (II) chloride solution.

Since the substrate surface has to be washed after the reduction of the ionogenic palladium, it can be assumed that a gel of tin hydroxide is formed, which contributes to the additional fixation of the palladium.

In the subsequent process, the excess protective colloid must be removed from the substrate surface so that a reduction in the metal ions, e.g. Copper, nickel, gold and cobalt in the metallization bath is possible through the catalytic action of active palladium centers on the substrate surface.

The known methods for electroless metallization of materials thus consist of a relatively large number of process steps and also have the disadvantage that they are limited to substrates which, because of their physical nature or chemical structure, enable chemical or physical roughening.

The object of the present invention was to provide a new, gentle and procedurally simple method for activating substrate surfaces for the purpose of electroless metallization, with which even surfaces that are difficult to metallize can be provided with a well-adhering metal coating, preferably without prior etching.

The invention therefore relates to a method for activating substrate surfaces for the purpose of electroless metallization, the surface to be metallized being wetted with an organometallic compound of elements of the 1st subgroup and 8th group of the periodic table of elements which is homogeneously distributed in a solvent, in particular an organic solvent , the solvent is removed and the organometallic compound adhering to the surface to be metallized is reduced, characterized in that the organic part of the organometallic compound, in addition to the groups required for metal bonding, has at least one further functional group from the series of carboxylic acid, carboxylic acid halide and carboxylic acid anhydride -, carbonic ester, carbonamide, carbonimide, aldehyde, ketone, ether, sulfonamide, sulfonic acid, sulfonate, sulfonic acid halide, sulfonic acid ester, vinyl sulfonic acid, acrylic acid, amino, hydroxyl, isocyanate, Olefin, acetylene, merc apto- and epoxy groups and the halogen-containing heterocycles and the higher-chain alkyl and alkenyl radicals from C ₈ .

The other functional group achieves very good adhesive strength on the substrate surface, this adhesive strength being due to a chemical reaction with the substrate surface or to adsorption.

Suitable higher-chain alkyl or alkenyl radicals are in particular oleic, linoleic, stearic or palmiting groups. Suitable groups of heterocycles are chlorotriazinyl, pyrazinyl, pyrimidinyl and quinoxaline groups.

If there is no anchoring by a chemical reaction, the adhesive strength can also be brought about by absorption of the organometallic activators on the substrate surface, the causes of the adsorption being e.g. Hydrogen bonds or van der Waalsche forces come into question.

It is appropriate to the functional groups that cause adsorption on the to match the respective substrate. For example, long-chain alkyl or alkenyl groups in the activator molecule improve the adhesive strength on substrates made of polyethylene or polypropylene. In contrast, activators with, for example, additional carbonyl or sulfone groups are particularly favorable for metallizing objects based on polyamide or polyester.

Functional groups such as carboxylic acid groups, carboxylic acid anhydride groups and ether groups are particularly suitable for anchoring the activator to the substrate surface by adsorption.

The groups of the organic part of the organometallic compound required for metal formation are known per se. For example, they are C-C or C-N double and triple bonds and groups that can form a chelate complex, e.g. OH, SH, CO, CS or COOH groups.

The organometallic compound can, for example, be dissolved or dispersed in the organic solvent, or it can also be a rubbing of the organometallic compounds with the solvent.

If the organometallic compound contains ligands which allow chemical fixation on the substrate surface, activation from the aqueous phase may also be possible.

• 1. Die verwendeten metallorganischen Verbindungen sollten an der Luft und gegenüber Feuchtigkeit stabil sein. Sie sollten in organischen Lösungsmitteln gut löslich, in Wasser aber schwach löslich sein. Sie sollten außerdem mit gebräuchlichen Reduktionsmitteln zu einer bei der stromlosen Metallisierung katalytisch wirksamen Verbindung reduzierbar sein.
• 2. Die Lösungen der metallorganischen Verbindungen in organischen Lösungsmitteln sollten an der Luft und gegenüber Feuchtigkeit stabil sein.
• 3. Das organische Lösungsmittel sollte leicht entfernbar sein.
• 4. Bei der Reduktion der organometallischen Verbindung dürfen keine Liganden frei werden, die die Metallisierungsbäder vergiften.
• 5. Die reduzierten aktiven Keime sollten in wäßriger Lösung fest an der Oberfläche haften, um eine Zersetzung der Bäder durch eingeschleppte Metalle zu verhindern.

However, without restricting the scope of the invention, it is advisable to comply with the following conditions when carrying out the process on an industrial scale:

• 1. The organometallic compounds used should be stable in air and moisture. They should be readily soluble in organic solvents, but slightly soluble in water. They should also be reducible with customary reducing agents to form a compound which is catalytically active in the electroless metallization.
• 2. The solutions of the organometallic compounds in organic solvents should be stable to air and moisture.
• 3. The organic solvent should be easily removable.
• 4. When reducing the organometallic compound, no ligands that poison the metallization baths must be released.
• 5. The reduced active germs should adhere firmly to the surface in aqueous solution to prevent decomposition of the baths by imported metals.

The process according to the invention is generally carried out as follows:

An organometallic compound of elements of subgroups 1 and 8 of the periodic table, in particular of Cu, Ag, Au, Pd and Pt with an additional functional group, is dissolved in an organic solvent. Mixtures of compounds can of course also be used. The concentration of organometallic compound should be between 0.01 g and 10 g per liter, but in special cases can also be below or above.

In particular, polar, protic and aprotic solvents such as methylene chloride, chloroform, 1,1,1-trichloroethane, trichlorethylene, perchlorethylene, acetone, methyl ethyl ketone, butanol, ethylene glycol and tetrahydrofuran are suitable as organic solvents.

Mixtures of the above solvents and blends with other solvents such as gasoline, ligroin, toluene, etc. can of course also be used. With the solutions according to the invention, the surfaces of the substrates to be metallized are wetted with these solutions, the duration of action preferably being 1 second to 10 minutes. Methods such as immersing the substrate in the solutions or spraying substrate surfaces with the activation solutions are particularly suitable for this purpose. Of course, with the new process it is also possible to apply the activation solutions by stamping or by printing processes.

Suitable substrates for the process according to the invention are e.g. Steels, titanium, glass, quartz, ceramics, carbon, paper, polyethylene, polypropylene, ABS plastics, epoxy resins, polyesters and textile fabrics, threads and fibers made of polyamide, polyester, polyolefins, polyacrylonitrile, polyvinyl halides, cotton and wool, and mixtures thereof or from copolymers of the monomers mentioned.

After wetting, the organic solvent is removed. Low-boiling solvents are preferably evaporated, e.g. removed in vacuum. For higher boiling solvents other methods, such as extraction with a solvent in which the oragnometallic compounds are insoluble, are appropriate.

The surfaces pretreated in this way must then be activated by reduction. The reducing agents customary in electroplating, such as hydrazine hydrate, formaldehyde, hypophosphite or boranes, can preferably be used for this purpose. Of course, other reducing agents are also possible. The reduction is preferably carried out in aqueous solution. However, other solvents such as alcohols, ethers, hydrocarbons can also be used. Of course, suspensions or slurries of the reducing agents can also be used.

The surfaces activated in this way can be used directly for electroless metallization. However, it may also be necessary to rinse the surfaces of the reducing agent residues.

A very particularly preferred embodiment of the invention The method consists in that the reduction in the metallization bath is carried out immediately with the reducing agent of the electroless metallization. This version represents a simplification of the electroless metallization that has not been possible until now. This very simple embodiment only consists of the three work steps: immersing the substrate in the solution of the organic compound, evaporating the solvent and immersing the surfaces thus activated in the metallization bath (reduction and Metallization).

This embodiment is particularly suitable for nickel baths containing amine borane or copper baths containing formalin.

Metallization baths which can be used in the process according to the invention are preferably baths with nickel salts, cobalt salts, copper salts, gold and silver salts or mixtures thereof with one another or with iron salts. Such metallization baths are known in the electroless metallization art.

The method according to the invention has the advantage of providing an adherent metal deposition by the subsequent electroless metallization, even without prior etching of the substrate surface.

On the other hand, it is often advantageous to swell or dissolve the substrate surfaces by treatment with a suitable solvent without, as in the case of etching, chemically changing or even degrading the polymer substrates.

Such processes are generally known and are described, for example, in the following patent literature: US Pat. Nos. 3,574,070, 3,445,350 and GB Pat. No. 1,124,556.

According to a particularly preferred variant of the method according to the invention, the activation and the swelling or the dissolving are carried out in one operation by the organometallic compound used for the activation in such solvent systems, which originate from swell or Solvents exist for the polymer substrate to be metallized, homogeneously distributed.

The organometallic activators can be in the form of real solutions, emulsions or suspensions.

The action of the activator systems with their characteristic swelling action on the substrates results in a type of "adhesion nucleation" which can perhaps be imagined in such a way that there are gaps accessible to the activation nuclei on the substrate surface, to which the metals deposited during electroless metallization are anchored .

The surface change caused by the "swelling adhesion nucleation" is noticeable by a change in the light separation, cloudiness, light permeability (in the case of mixed foils and plates), change in layer thickness or in scanning electron microscope images in the form of cracks, caverns or vacuoles.

The swelling agents suitable for the particular polymer substrate to be metallized must be determined on a case-by-case basis by means of appropriate preliminary tests. A swelling agent behaves optimally if it swells the surfaces of the substrates within reasonable times without completely dissolving the substrate or even negatively influencing its mechanical properties such as notch impact strength and without changing the organometallic activators.

Suitable swelling agents are also solvents specified in the abovementioned patent literature, for example the so-called 9 solvents or their blends with precipitants, such as a "Polymer Handbook" J. Brandrup et al, New York, IV, 157-175, (1974) .

Suitable swelling or solvents are lower and higher alcohols, aldehydes, ethers, ketones, halogenated hydrocarbons, simple or saturated hydrocarbons, organic acids, esters or their halogenated derivatives, liquid gases such as butane, propylene, 1,4-cis-butadiene.

Mixtures of these solvents and blends with other solvents such as gasoline, ligroin, toluene, n-hexane, etc. can of course also be used. In order to achieve a better interaction between the substrate surface and the adhesive seeding medium, such media can be provided with organic and / or inorganic additives. For this purpose, anionic emulsifiers, such as, for example, alkali salts of palmitic acid, stearic acid, oleic acid, salts of sulfonic acids, which are produced on the basis of paraffins containing 6-20 carbon atoms, by sulfochlorination; non-ionic emulsifiers which can be prepared, for example, by ethoxylation of long-chain alcohols or phenols; cationic emulsifiers, such as salts of long-chain, particularly unsaturated amines with 12 to 20 C atoms or quaternary ammonium compounds with long-chain olefins or paraffin esters; Protective colloids based on macromolecular compounds, such as gelatin, pectins, alginates, methyl cellulose, ionic and neutral polyurethane dispersions or their oligomeric derivatives, polyvinyl alcohols, polyvinyl pyrrolidone, polymethyl vinyl acetate; finely divided water-soluble minerals such as alumina, diatomaceous earth, calcium phosphates; Alkali and alkaline earth salts CaC12, MgS0 ₄ , K ₃ P0 ₄ well suited.

The amount of the additives listed above can be varied, based on the medium at hand, from 0.01 to 20% by weight.

To increase the resistance of the organometallic activators in the organic media, it may be necessary to additionally enrich them with up to 10% of dimethylformamide, dimethyl sulfoxide or tetramethyl urea.

To increase the germination effect of the organic media, it may be necessary to add inorganic compounds such as CI ₂ , HCI, H ₂ 0, HF, HJ, H _Z S0 ₄ , H ₃ P0 ₄ , H ₃ P0 ₃ , H ₃ SO ₃ To add boric acids, NaOH or KOH. Their amount can be varied from 0.1 to 30% by weight (based on the respective medium), the additions of inorganic compounds being able to be above or below in some cases. In order to achieve a uniform distribution of these inorganic additives in the organic media, it may be necessary to add small amounts of water as a solubilizer.

With the media according to the invention, the surfaces of the substrates to be metallized are wetted with these media, the exposure time preferably being 1 second to 90 minutes. Methods such as immersing the substrate in the media or spraying, vapor deposition of substrate surfaces with the activation media are particularly suitable for this purpose.

Furthermore, it is also possible with this adhesive seeding process to apply the activation solutions by stamping or by printing processes.

The adhesive seeding according to the invention can be carried out at a temperature of from -20 ° C. to 100 ° C., low temperatures being preferred for low-boiling solvents and chemically susceptible substrates, whereas chemically resistant substrates require higher temperatures. In exceptional cases, seeding can also be carried out at lower or higher temperatures from -20 ° C or 100 ° C. Temperatures from 0 ° C to 80 ° C are preferred.

After wetting the substrate surfaces, the solvent is removed as described above.

In order to increase the deposition rate of the metallization reaction, an additional activation of the substrate surfaces in the activation medium, which is a precipitant for the polymer material, can be carried out. Such precipitants are known and can be found in the "Polymer Handbook", IV, 241-267, which has already been given.

example 1

A 10 x 10 cm square of a knitted fabric made of a polyester polymer (100% polyethylene terephthalate) is at room temperature for 10 seconds in an activation bath which consists of 0.4 g of 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (II) chloride and 1 I CH ₂ Cl ₂ is prepared, dipped, dried at room temperature and then 10 minutes in an aqueous alkaline nickel plating bath which contains 113.5 g of dimethylamine borane, 30 g of nickel chloride and 10 g of citric acid and with conc. Ammonia solution is adjusted to pH 8.2, nickel-plated without current. After about 60 seconds, the surface begins to turn shiny metallic and after 10 minutes 12 g / m2 had been deposited.

Example 2

A 150 x 100 mm injection-molded ABS plate (acrylonitrile-butadiene-styrene graft copolymer) is degreased in an aqueous 15% by weight sodium hydroxide solution, neutralized with distilled water, for 30 seconds in an activation solution of 0.8 g of 4-cyclo- Hexen-1,2-dicarboxylic acid anhydride silver (I) nitrate immersed in 11 methanol, dried at room temperature and then nickel-plated according to Example 1. The specimen is covered with a very fine nickel layer after only 60 seconds. After approx. 10 minutes the chemical nickel layer has an average thickness of approx. 0.20 µm. After the test specimen was removed from the chemical metallization bath, rinsed with distilled water, it was placed as a cathode in a galvanic copper bath and galvanically reinforced to a thickness of approx. 6.6 µm at 0.5 A / dm ² in 30 minutes.

Example 3

A 120 x 120 mm square of a cotton fabric is activated for 20 seconds according to Example 1 and then nickel-plated. A piece of shiny metallic material with a metal coating of about 11% by weight of nickel is obtained.

Example 4

A 35 x 100 mm rectangle made of a polyester film is activated for 20 seconds in accordance with Example 1 and nickel-plated for 7 minutes after the solvent has evaporated. A shiny metallic foil with a 0.15 μm thick nickel is obtained.

Example 5

A 40 x 60 mm rectangle of a roughened polycarbonate film with 10% by weight of polybutadiene is immersed in a solution of 0.5 g of 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium dichloride in 1 liter of methanol, dried and then according to the example 1 nickel-plated.

After 7 minutes, an adherent, metallic, shiny, 0.2 µm thick nickel layer had been deposited. This layer was switched as a cathode in a galvanic copper bath and reinforced with galvanic copper at 1.0 amperes to 30 µm within 30 minutes. The galvanic copper bath is made up of 200 g of C _U S0 ₄ and 30 g of H ₂ S0 ₄ (96%), made up to 1 1 with distilled water.

Example 6

A 150 x 150 mm square of a cotton fabric is placed in a 0.5 g solution for 30 seconds
Isobutyl vinyl ether palladium dichloride dipped in 111,1,1-trichloroethane, dried at room temperature and then nickel-plated in a nickel bath according to Example 1 for 20 minutes.

After about 20 seconds the surface begins to turn dark and after 10 minutes a shiny metallic nickel layer had been deposited.

Example 7

A 100 x 100 mm square of a glass fiber reinforced epoxy resin plate is made with a solution of 0.6 g
Sprayed isobutyl vinyl ether palladium dichloride in 1 11,1,1-trichloroethane, dried at room temperature and then nickel-plated in a chemical nickel bath according to Example 1. The surface of the plate begins to turn dark after only 30 seconds, after 60 seconds it is covered with a fine nickel layer and after approx. 10 minutes the chemically deposited nickel layer has a thickness of approx. 0.2 µm.

Example 8

A 150 x 50 mm rectangle of a polyethylene plastic part is immersed in an activation bath which is made up of 0.75 g of 9-octadecen-1-olpalladium dichloride and 1 I1,1,1-trichloroethane, and then in a chemical nickel bath according to the example 1 nickel-plated.

A shiny metallic plastic part is obtained, which is switched in a galvanic semi-gloss nickel bath as the cathode at 50 ° C. and 1 ampere in 30 minutes to a thickness of approximately 8.1 μm.

• 4-Cyclohexen-1,2-dicarbonsäureanhydrid- palladium(II)chlorid:
• 4-Cyclohexen-1,2-dicarbonsäureanhydrid wird in der dreifachen Menge Dimethylformamid gelöst, im Verlaufe von 2 Stunden mit der äquimolaren Menge Acetonitrilpalladiumdichlorid bei 40° C versetzt. Dimethylformamid und Acetonitril werden bei 45°C/25 mbar abdestilliert. Man erhält mit 90 %iger Ausbeute einen bräunlichen Feststoff vom Schmelzpunkt 53-54° C.

The organometallic compounds used in the examples are obtained as follows:

• 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (II) chloride:
• 4-Cyclohexene-1,2-dicarboxylic acid anhydride is dissolved in three times the amount of dimethylformamide, and the equimolar amount of acetonitrile palladium dichloride is added at 40 ° C. in the course of 2 hours. Dimethylformamide and acetonitrile are distilled off at 45 ° C / 25 mbar. A brownish solid with a melting point of 53-54 ° C. is obtained in 90% yield.

Isobutyl vinyl ether palladium dichloride is obtained in an analogous manner from the
Acetonitrile palladium dichloride and
Obtained isobutyl vinyl ether, melting point: 57-60 ° C.

Example 9

A polymer plate made of polyamide 6 with 30% by weight of glass fibers is degreased in 20% sodium hydroxide solution at room temperature (RT). Subsequently, it is immersed for 8 minutes in an adhesive seeding solution consisting of 40% by weight hydrochloric acid (37% pure), 60% by weight methanol and 0.9 g / l 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (II) chloride exists. Then the sample is mixed for 20 minutes
Metallization bath, which contains 30 g / l nickel sulfate, 3.8 g / l dimethylaminobrorane, 10 g / l citric acid and is adjusted to pH 7.6 with concentrated aqueous ammonia solution. The adhesive strength of the metal pad, which is determined by the pull-off force according to DIN 53494, is -6N / 2.5 cm.

Example 10

A polymer plate made of polyamide 6 with 35% by weight of butadiene graft polymer is degreased at RT in 15% sodium hydroxide solution. It is then prepared for 10 minutes in a bath which consists of 90 g of HCl (traveling 37%), 410 g of ethylene glycol and 0.5 g of 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (II) chloride is activated and then metallized in a metallization bath according to Example 13 over the course 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 11

A test plate 10 x 10 cm, 3 mm layer thickness, of an ABS (acrylonitrile-butadiene-styrene) plastic is degreased at room temperature with 22% NaOH solution. The plate is then immersed for 10 minutes in a solution containing 700 ml of methanol, 100 ml of acetoacetic ester, 50 ml of DMF (dimethylformamide) and 0.9 ml of 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (11) chloride. The plate is washed with methanol, dried and then neutralized in an electroless nickel plating bath according to Example 13. After 25 minutes, an even, matt Ni coating has deposited. The adhesive strength, determined by the peel force according to DIN 53494, is 5N / 2.5 cm.

Claims (9)

1. Process for the activation of substrate surfaces for the purpose of currentless metallisation, in which the surface to be metallised is wetted with an organometallic compound of elements of subgroup 1 and group 8 of the periodic system of elements homogeneously distributed in a solvent, the solvent is removed and the organometallic compound adhering to the surface to be metallised is reduced, characterised in that the organic part of the organometallic compound contains, in addition to the group required for the formation of the metal, at least one further functional group from the series comprising the carboxylic acid, carboxylic acid halide, carboxylic acid anhydride, carboxylic ester, carboxamide, carboximide, aldehyde, ketone, ether, sulphonamide, sulphonic acid, sulphonate, sulphonic acid halide, sulphonic acid ester, vinyl sulphonic acid acrylic acid, amino, hydroxyl, isocyanate, olefin, acetylene, mercapto and epoxide groups and the halogencontaining heterocycles and the higher-chain alkyl and alkenyl radicals with C₈ and more.

2. Process according to Claim 1, characterised in that the additional functional groups are carboxylic acid and carboxylic acid anhydride groups.

3. Process according to Claim 1, characterised in that the organometallic compound is dissolved or dispersed in the solvent in a quantity of 0.01 to 10 g/l.

4. Process according to Claim 1, characterised in that the solvent is a pure organic solvent or mixtures or blends of several organic solvents.

5. Process according to Claim 1, characterised in that the subatrate surfaces to be metallised are activated without prior etching.

6. Process according to Claim 1, characterised in that the substrate surfaces are treated with a swelling agent.

7. Process according to Claim 1 or 6, characterised in that the swelling agent is in the activating bath.

8. Process according to Claim 1 or 6, characterised in that e-solvents or blends thereof with precipitants are used as the swelling agents.

9. Process according to Claim 1 or 6, characterised in that the swelling agent additionally contains emulsifiers and/or watersoluble minerals - preferably CaC1₂ or organic and/or inorganic acids such as HCI or CH₃COOH.