Process for producing metal-coated materials

The invention relates to a process for the production of metallized materials and in particular to such a process in which the desired metal is deposited on the material in a non-electrochemical manner.

Applying metal layers to non-conductive materials or conductive materials, such as metals, is a technique required in many industries and practiced in a variety of variations. The aim of this treatment is, in particular, to obtain antistatic or conductive surfaces or to provide electromagnetic shielding. Further, metallizing may serve to provide a desired visual effect, such as a metallic "look", or to obtain tempered or more abrasion resistant surfaces. Finally, the metallization of material surfaces also has a great importance in the production of printed circuit boards.

To carry out the metallization, ie the application of the metal to the material, in addition to electrochemical and non-electrochemical processes are known, which are also referred to as chemical deposition methods. Such chemical processes are usually preceded by a suitable surface treatment of the material and are known for various metals such as An, Ag, Pd, Cu, Sn or Ni. Frequently, after previous chemical metallization, additional electrochemical methods are used to increase the thickness of the deposited metals.

From Journal of Vacuum Science and Technology Part B, Vol. 9, No. 6, November 1991, pages 3428-3431, it is known that polyaniline can be used for non-electrochemical deposition of noble metals. For this purpose, the polyaniline is immersed in an aqueous solution of palladium or silver salt solution, whereupon the noble metal ions are reduced and deposit thin layers of the noble metal on the polyaniline.

The known chemical methods, however, lead in various applications to poor properties in the applied metal layers or metallized materials. Thus, the layers obtained are often irregular or they show a lack of elasticity or too high brittleness. Furthermore, the known methods are not very efficient because they often require the use of large quantities of mostly toxic chemicals.

The invention is therefore based on the object to provide a non-electrochemical process for the production of metallized materials available, which is superior to the known methods with regard to the above-mentioned aspects.

This object is surprisingly achieved by the method according to claims 1 to 10 according to the invention.

The invention also relates to the use of intrinsically conductive polymers in the non-electrochemical application of metals to materials according to claims 11 and 12.

The inventive method for the production of metallized materials is characterized in that one<ul id="ul0001" list-style="none"><li>(a) providing the material to be metallized with a coating containing intrinsically conductive polymer,</li><li>(b) activating the intrinsically conductive polymer by reduction and</li><li>(c) applying the metal to the material in a non-electrochemical manner by contacting the coated material with a solution containing ions of the metal.</li></ul>

Among the "intrinsically conductive polymers" used in the process are understood as meaning those organic polymers which contain polyconjugated bonding systems, eg Double bonds, aromatic or heteroaromatic rings or triple bonds. Examples of such polymers are polydiacetylene, polyacetylene (PAc), polypyrrole (PPy), polyaniline (PAni), polythiophene (PTh), polyisothianaphthene (PITN), polyheteroarylenevinylene (PArV), where the heteroarylene group eg Thiophene or pyrrole, poly-p-phenylene (PpP), polyphenylene sulfide (PPS), polyperinaphthalene (PPN), polyphthalocyanine (PPhc) and their derivatives (eg composed of substituted monomers), their copolymers and their physical mixtures. They can be present in different states which are described by different empirical formulas and can generally be converted into one another in a reversibly reversible manner by reactions such as oxidation, reduction, acid / base reaction or complex formation. These reactions are occasionally also referred to in the literature as "doping" or Called "compensation". At least one of the possible states is electrically very good conductive, eg with a conductivity of more than 1 S / cm (as a pure substance) so that it is possible to speak of intrinsically conductive polymers. Sometimes the intrinsically conductive polymers are also referred to in the literature as "organic metals".

A good overview of intrinsically conductive polymers already synthesized to date, which are suitable according to the invention, can be found, for example, in Synthetic Metals, Issues 17, 18 and 19 (1987).

The coating applied in step (a) may in particular be a polymer blend containing intrinsically conductive polymer. In addition to intrinsically conductive polymer, the polymer blends used according to the invention contain further polymers, copolymers or polymer blends, such as Polyamides, polyesters, polyethers, such as polyethylene oxides, copolymer latexes on an aqueous basis, such as Vinyl acetate butyl acrylate, or other copolymer latexes, and / or polyvinyl alcohols. Particularly preferred further polymers are polyamides.

Advantageous polymer blends have a content of preferably 0.1 to 45 wt .-% and particularly preferably 5 to 35 wt .-% intrinsically conductive polymer.

It is also possible that pure intrinsically conductive polymers are used as the coating.

It has also proven to be particularly advantageous if the intrinsically conductive polymer is used in the form of a dispersion. This may be a dispersion in organic solvents, such as alcohols or N-methylpyrrolidone, or in aqueous solvents. The dispersions may also contain binders, such as polymeric or film-forming binders, for example the other polymers given above as a component of polymer blends.

Polyaniline is used as the preferred intrinsically conductive polymer.

The application of the coating can be carried out by conventional methods, such as, for example, mechanical application by means of a doctor blade or immersion in solutions or dispersions of intrinsically conductive polymer.

In process step (b), the intrinsically conductive polymer is activated by reducing it. The reduction z. B. by electrochemical means, that is done with the help of an externally applied electric current. However, it is preferred that the reduction be carried out by use of chemical reducing agents. As chemical reducing agents are in particular H₂, Hydrides, such as borohydrides, eg BH₃, and / or with respect to the intrinsically conductive polymer reducing metals, such as iron, aluminum or copper, in question. Whether a metal has a reducing effect on the polymer, of course, depends on the specific conditions under which the reduction takes place. For example, the pH value and the presence of complexing agents can exert an important influence.

Hydrazine and hydrazine compounds, such as hydrazine salts, for example hydrazine sulfate, have proven to be particularly preferred reducing agents.

To improve the stability and reproducibility of the activation, the reduction is preferably carried out in a degassed, ie oxygen-poor or -free medium. However, special applications of the process are conceivable in which the presence of oxygen is not detrimental but even desirable.

In the case of the polyaniline preferably used as an intrinsically conductive polymer, the reduction is frequently also recognizable by a color change which results from the formation of the reduced form of the polyaniline, the so-called leucoemeraldine.

In step (c), the selected metal is applied to the material in a non-electrochemical manner by contacting the coated material with a solution containing metal ions.

Usually, this process step is carried out after step (b). However, it is also possible that the non-electrochemical application of the metal to the coated material takes place at the same time as the reduction. An example of this is the tinning according to the invention of copper, as explained in more detail below and in the examples. In some cases, however, the simultaneous execution of (b) and (c), for example due to the incompatibility of chemicals used in (b) and (c) with each other or because of procedural aspects not be desired.

By application in a "non-electrochemical manner" is meant a process in which application is not by use of an externally applied electrical current. Rather, the material provided with the polymer-containing coating material is brought into contact with the metal ion solution, for which usually simple immersion in the solution is sufficient.

The solution is preferably one of monovalent or divalent cations of the metal, and in particular an aqueous solution having a pH of &lt;7 is used.

The method according to the invention permits the simple and efficient metallization of materials with metals, and has proved to be particularly advantageous when applying Cu, Ag, Pd, Sn, Pt and / or Ni. Particularly preferably, the method is used for the application of Cu, Ag or Sn.

As materials are primarily plastics of all kinds, especially those containing polyamide or polyethylene terephthalate, glasses or ceramics in question. However, it is also possible to metallise other materials, such as metallic materials, using the method according to the invention.

The mechanism of the method according to the invention is assumed that the reduced intrinsically conductive polymer of the coating acts as an electron transfer agent and thus as a catalyst and the reducing agent used does not interact directly with the ions of the metal to be deposited or these are not directly reduced. The electron transfer from the intrinsically conductive polymer to the metal cations then results in a deposition of elemental metal on the coated material. The concomitant oxidation of the conductive polymer leads at least partially to a regeneration of the conductive polymer used and opens up the possibility of subjecting it again to the reduction and deposition steps (b) and (c). In view of this proposed reaction mechanism, one can thus speak of a catalytic activity of the intrinsically conductive polymer.

Particularly illustrative of the surprising catalytic functioning of the coating with intrinsically conductive polymer is the tin deposit according to the invention on copper.

In the conventional non-electrochemical tinning of copper is usually used z. B. methanesulfonate thiourea-containing Sn²⁺-Solutions. The task of the thiourea is evidently to allow the complexation with Cu (+ I) the dissolution of the copper, since methanesulfonic acid alone does not dissolve or dissolve copper. Further, due to the more negative potential of the Cu (I) -thiourea complex relative to uncomplexed Cu (I), electron transfer to Sn²⁺ and thus its reduction to Sn⁰ allows.

Expressed in moles, in this tinning of copper theoretically twice as much Cu must be dissolved as one wants to deposit Sn. In fact, a careful analysis of the increase in Cu (II) concentration and the decrease in Sn (II) concentration in the tinning solution during the tinning of larger Cu surfaces in operational applications instead of Cu (II): Sn (deposited) Ratio of 2 is one of 1.22. The reason for this is unknown in the literature.

As Fig. 2 shows that the increase of the Cu (II) and the decrease of the Sn (II) concentration in the conventional non-electrochemical tin plating deviates from the initially correct linear development above certain concentrations. This is the phenomenon known from the technical literature and the instructions of the manufacturers, that the tinning above a Cu concentration of 0.08 mol / l or below a Sn (II) concentration of 0.1 mol / l no longer goes as desired, and therefore the tinning can not be used then, but must be renewed. For explanation it is stated that outside of the recommended concentration ranges, instead of pure tin layers, unwanted intermetallic phases (Sn_x/ Cu_y). The function of the tin on the copper layer is then no longer guaranteed.

The deviations from the linear behavior are particularly strong when, instead of the total concentration of Cu (II) - which, for chemical reasons, was not converted until a few days, when the total amount of Cu (I) was converted by atmospheric oxygen to Cu (II), determine the amount of Cu (II) that occurs immediately during the coating process. In a way, the dynamics of the Cu (I) / Cu (II) reactions are recorded, with the difference between the total amount of dissolved copper ions and those we call "dynamic" being Cu (I). This curve is labeled "Cu (I) after tinning" in Figure 2, and is especially nonlinear once the critical Cu concentration is reached.

If, instead of uncoated copper surfaces, those which, according to the invention, are provided with a thin coating of conductive polymer which is reduced by the copper under the tinplating conditions, show a completely different behavior. Now, the Cu (II): Sn (deposited) ratio approaches the ideal value of 2 and is 1.63. In addition, as Fig. 1 shows, the course of the increase of the total Cu (II) and also the dynamic Cu (I) concentration and the decrease of the Sn (II) concentration over the entire concentration range linearly. Even well above the critical concentrations, the concentration development is clearly linear without changing the slope. This behavior in the tinning according to the invention is discussed in more detail in Example 3.

These results are in parallel with those resulting from the analysis of the obtained layer thickness of tin. This shows that the layer thickness in the tin plating of copper without coating with intrinsically conductive polymer from about 0.6 m²/ l (surface copper per volume of tinning solution) decreases significantly, while it remains substantially constant in the case of tinning performed according to the invention.

It follows as a practical advantage of the method according to the invention that no intermetallic phases are deposited, which could reduce or cancel the intended function of the tin layer, and more than twice as large a surface can be coated per liter of tinning used, as with conventional chemical deposition methods is possible.

The case of tinning copper by the process according to the invention clearly shows the catalytic function of the intrinsically conductive polymer used. It is believed that in this particular metallization, for example in the case of polyaniline as a polymer, that of Cu⁰ is reduced to leucoemeraldine, which then in turn Sn²⁺ to Sn⁰ reduces, while the existing oxygen Cu to Cu²⁺ oxidized.

In any case, the immersion of a coated with the polymer copper plate in saline water already leads to the reduction of the polyaniline, which can be determined at sufficiently large layer thicknesses of polyaniline, eg 1-5 microns, also visually based on the decolorization on the formation of the colorless leucorneraldine is due to reduced form.

Finally, the invention also relates to the use of intrinsically conductive polymers in the non-electrochemical application of metals to materials by<ul id="ul0002" list-style="none"><li>(a) providing the material to be metallized with a coating containing intrinsically conductive polymer,</li><li>(b) activating the intrinsically conductive polymer by reduction and</li><li>(c) applying the metal to the material in a non-electrochemical manner by contacting the coated material with a solution containing ions of the metal.</li></ul>

The invention will be explained in more detail below with reference to examples.

Examples

Example 1:

Metallization of polyamide with copper

A polyamide-based polymer blend containing 4% by weight polyaniline, viz <i>Ormecon 900187/34</i> from Ormecon Chemie, Ahrensburg, was based on a polyamide film <i>PA6 Ultramid B3L</i> BASF applied with a doctor blade in a layer thickness of 100 microns. The coating was green. The film was dried at 80 ° C for 20 minutes.

For metallization, the coated film was immersed in 1 N sodium hydroxide solution containing 13 g / l of hydrazinium sulfate and stored there at room temperature for 24 hours under nitrogen for reduction. When immersed in the reduction medium, the coating immediately discolored deep blue. As the reduction progressed, the color of the polyaniline layer turned gray. After being withdrawn from the reducing solution, the film was rinsed under nitrogen with distilled water and immediately transferred to a solution of 0.1 N copper dosesylate / 0.01 N dodecylbenzenesulfonic acid having a pH of 4. Here it was left under nitrogen for 5 hours for copper deposition. The color of the surface turned green-brown. After subsequent rinsing with distilled water, the surface was immersed in aqueous ammonia solution for one minute to remove adherent copper salts. After renewed rinsing with water, the bronze-colored foil was dried in air.

All the above treatments were carried out at room temperature unless otherwise specified, and the solutions used were made fresh before use, degassed and purged with nitrogen for 5 minutes.

By X-ray fluorescence analysis with Ge-target excitation at 25 KV and 1.0 mA, the copper deposited on the polyaniline could be identified by peaks at 8.05 and 8.91 KeV.

Repeated repetition of the chemical redox processes, ie reduction and metal deposition, made it possible to increase the amount of copper deposited.

Example 2:

Metallization of polyethylene terephthalate with silver

A polyamide-based polymer blend containing 4% by weight of polyaniline, namely the varnish <i>Ormecon 900187/34</i> from Ormecon, Ahrensburg, was applied with a doctor blade in a layer thickness of 50 microns on a polyethylene terephthalate (PET) film. The green-coated PET film was metallized with silver after a drying time of 10 minutes at 80 ° C.

For this purpose, the coated PET film was immersed in sodium hydroxide solution containing 30 g / l hydrazinium sulfate. The pH of the solution was 9 to 10. The film was stored under nitrogen for 12 hours for reduction in this solution. After the coating of the film immediately turned blue upon immersion in the solution, it had a yellow color after reduction. After withdrawing from the reducing solution, the film was rinsed under nitrogen with distilled water and immediately immersed in a 0.33 molar para-toluenesulfonic acid solution of pH 1 containing 11.2 g / l of silver nitrate for 30 minutes for silver deposition immersed. The color of the surface of the film turned green. After a few minutes, a silver deposit was already visible. After rinsing with distilled water, the film was dried in air.

All the above treatments were carried out at room temperature unless otherwise specified, and the solutions used were made fresh before use, degassed and purged with nitrogen for 5 minutes.

Using X-ray fluorescence analysis, the silver deposited on the polyaniline coating was clearly identified by peaks at 2.98, 3.14 and 3.23 KeV. In addition, only the sulfur peaks at 2.30 and 2.47 KeV were evident, which came from the counterions of polyaniline.

Example 3

:

Chemical deposition of tin on copper

The surface of copper plates was chemically tinned. The tinning according to the invention was carried out with coating of copper plates with an aqueous dispersion of polyaniline, for example Ormecon 900236/04 the company Ormecon Chemie, Ahrensburg. For comparison, the tinning was carried out without polyaniline coating.

<u>execution</u>

The area of ​​the copper plate, which was to be tinned, was determined by measuring. To degrease the surface and to remove the oxide layer or a zinc or chromate layer protecting the copper from tarnishing, microetching of the plate was performed. The copper plate was immersed at room temperature for two minutes in the commercial acid pickling Circuposit Etch 3330 based on sulfuric acid and peroxide from Shipley, Germany. Subsequently, the plate was rinsed with water and applied to a polyaniline coating for one minute in an aqueous polyaniline dispersion, namely, diluted 1:19 with water <i>Ormecon 900236/04</i>Concentrate (Ormecon Chemie, Ahrensburg). After rinsing with water, the plate became in the tinning solution<i>Tinposit LT-34 Immersion Tin</i>Solution (Shipley, Germany) at 50 ° C non-electrochemically tinned by immersing in this solution. The tinning solution develops Sn²⁺Ions, phenolsulfonic acid and thiourea. The deposition reaction commenced immediately upon immersion of the plate. The plate was pulled out of the tinning bath after 20 minutes, rinsed with water and dried. The surface was now covered with a silky matt, silver-colored tin layer.

For comparison, the above steps were repeated with the change that a polyaniline coating was not applied.

<u>analytics</u>

<u>A. Tin determination in the Tinposit LT-34 immersion tin solution</u>

Tin, which was in 2-valent form, was quantified in solution buffered with sodium acetate directly with xylenol orange as an indicator by titration with Titriplex III.

Execution of the determination

2 ml of <i>Tinposit LT-34 Immersion Tin</i>Solution were diluted to 100 ml with water, with 1 ml conc. HCl and adjusted with sodium acetate to a pH of about 4. After addition of xylenol orange indicator trituration, titration was carried out with Violet's 0.1 N Titriplex III solution until the last lasting color change to light yellow.

calculation

1 ml 0.1 mol / l Titriplex III solution = 11.869 mg Sn

<u>B. Copper Determination in the Tinposit LT-34 Immersion Tin Solution</u>

Copper, which was present in divalent form, was determined spectrophotometrically by addition of ammonia as a copper tetrammine complex.

Execution of the determination

0.5 ml of <i>Tinposit LT-34 Immersion Tin</i>Solution was concentrated with 5 ml of conc. Ammonia (25%, very pure), well shaken, and the white precipitate of Sn (OH)₂ (actually tin-II-oxide hydrate complicated composition) was filtered after about 5 minutes with a filter crucible (porosity 3). The clear filtrate was measured in a 10 mm glass cuvette in the UV / Vis spectrophotometer in the range of 1000 to 400 nm. As a reference spectrum, a pure ammonia solution (25%) was used. From the extinction of the maximum at about 630 nm, the copper ion concentration was determined by means of a calibration line.

<u>calculation</u>

Calibration line:<maths id="math0001" num=""><math display="block"><mrow><mtext>y = 0.0913x + 0.035</mtext></mrow></math><img file="EP0807190B1_D0001.tif" /></maths> With<maths id="math0002" num=""><math display="block"><mrow><mtext>y = measured absorbance</mtext></mrow></math><img file="EP0807190B1_D0002.tif" /></maths> and<maths id="math0003" num=""><math display="block"><mrow><msup><mrow><mtext>x = Cu</mtext></mrow><mrow><mtext>2+</mtext></mrow></msup><mtext> in g / l</mtext></mrow></math><img file="EP0807190B1_D0003.tif" /></maths>

<u>C. Tin determination on the copper surface</u>

To determine the layer thickness of the deposited on the copper tin, the tin was dissolved with acid and quantified in the resulting solution by titration with Titriplex III.

Execution of the determination

The tinned copper plate was dipped in concentrated hydrochloric acid at 50 ° C for 10 minutes and then rinsed with water. Rinse water and the amount of acid used for stripping were combined, made up to 100 ml with water and brought to a pH of about 1 with caustic soda cookies. A pH of about 4 was then adjusted with sodium acetate, and after addition of xylenol orange indicator trituration, titration was carried out with Violet's 0.1N Titriplex III solution until the last lasting color change to light yellow.

<u>Measurement results</u>

The analytical studies have determined the tin and copper content of the <i>Tinposit LT-34 Immersion Tin</i>Solution in g / l for the respective m² tinned copper plate surface per liter of solution determined. The decrease in the tin content and the increase in the copper (II) concentration were converted into mol / l for better comparison. The copper (II) concentration was determined immediately after removal of the tinned plates and 48 hours after the tinning bath had been air-dried at room temperature. The tin content did not change over this period, while the copper (II) content showed a strong increase. This presumably resulted from the copper (I) ions present in the tinning solution, which had been slowly oxidized by air oxygen to copper (II) ions. In the spectrophotometric detection of the copper concentration only Cu (II) ions were detected. From the difference in the copper (II) concentration after immediate removal and after 48 hours, the proportion of copper (I) ions in the solution could be determined directly after tinning.

In FIGS. 1 and 2, the tin decrease and copper increase of the Tinposit LT-34 Immersion Tin solution against the m² applied to tinned Rupferoberfläche per 1 used solution. FIG. 1 shows the behavior of the copper plate metallized in accordance with the invention, and FIG. 2 shows the copper plate conventionally metallized for comparison, which was not provided with a polyaniline coating.

The comparison of Figures 1 and 2 shows that in the chemical tinning with a pretreatment in an aqueous polyaniline dispersion over the entire range, a linear increase in the copper concentration or a decrease in tin concentration is recorded. The tin deposition is carried out by applying a Polyanilinschicht even after exceeding the marked limit for the guaranteed by the manufacturer of the tinning solution range of validity (Sn content of the solution&gt; 18 g / l) with the same layer thickness. In tinning without polyaniline coating, however, occurs from about 0.45 m²/ tinned surface per l solution a negative deviation, and the amount of deposited tin decreases when exceeding the marked limit.