EP0530144A2 - Process for metallising plastic articles - Google Patents

Abstract

In a process for the partial and discontinuous metallisation of a plastic article by means of noble-metal particles, the plastic article containing a finely divided, homogeneously distributed filler selected from the group consisting of MnO, NiO, Cu2O, SnO and Bi2O3 is treated with an acidic aqueous solution of a noble-metal salt in such a manner that noble-metal particles are partly and discontinuously applied by electrochemical means to the plastic surface by suitable adjustment of the concentration of the acids, of the noble-metal salt and of the filler with respect to one another, and the article metallised in this way is treated with a metal by a conventional process in order to produce a continuous metal layer on the treated surface.

Description

The present invention relates to a method for the partial and discontinuous metallization of plastic objects with noble metal particles and subsequent metal coating by a conventional method, and to the coated plastic objects obtainable in this way.

The metallization of plastic surfaces plays an increasingly important role in various branches of industry. The electrically conductive coating of electrically insulating substrates is primarily in the electronic industry, e.g. important in the manufacture of printed circuits. Metallized plastic parts are also used in the production of decorative and / or reflective objects.

The usual method of metallizing plastics is the electrochemical deposition of metals on plastic surfaces. At least four process steps are necessary in that the plastic surface is pretreated chemically or mechanically in a first step and a discontinuous metal primer is applied in a second step; in a third step, a very thin continuous metallic layer is applied through a chemical amplification bath containing a metal salt and a reducing agent, and the substrate pretreated in this way is then placed in an aqueous solution of a metal salt for galvanic metallization, so as to obtain a thicker metal layer . The primer coating is e.g. applied so that the pretreated substrate is treated in an acidic tin salt solution and then metallized in an aqueous precious metal solution. Both bathrooms can also be combined

This method is quite complicated and has many individual steps that are characterized by delicate process conditions. While chemical or mechanical pretreatment often leads to damage to the substrate, problems often arise when the metal primer is applied due to the lack of wettability of the plastic surface by the primer solution. The primer layer so produced is of poor quality, discontinuous and poorly adherent. This and other special metallization processes are described in U.S. Patent No. 4,590,115.

In EP patent application No. 0417037 it is also proposed to carry out the metal coating continuously by treating the plastic article containing certain metal oxides (MnO, NiO, Cu₂O, SnO or Bi₂O₃) with an acidic aqueous solution of a noble metal salt. The metal layer produced in this way should have improved adhesion to the plastic surface. It is particularly important in this process that the solution bath is stirred optimally, otherwise certain parts of the object to be treated, in particular its cavities and the parts which are spatially unfavorably oriented in the metallization bath, are incompletely or unsatisfactorily metallized. According to this method, the pH of the noble metal salt solution should preferably be 0.5 to 3.5, the optimum being in a relatively narrow pH range of less than one pH unit. In addition, this process consumes a relatively high proportion of precious metal salts; these salts are expensive, which has an unfavorable process cost.

It has now been found that this process can be significantly improved if the surface of the plastic article to be treated is only partially and discontinuously metallized with precious metal particles and then coated with a metal by a conventional process; The new process can be carried out in a much broader acidity range, significantly smaller proportions of noble metal salts are consumed, and the articles obtained in this way are distinguished by excellent performance properties.

The present invention accordingly relates to a new method for the partial and discontinuous metallization of a plastic article with precious metal particles, according to which the plastic article containing a finely divided, homogeneously distributed filler selected from the group consisting of MnO, NiO, Cu₂O, SnO and Bi₂O₃ with an acidic aqueous solution of a noble metal salt is treated in such a way that noble metal particles are partially and discontinuously electrochemically applied to the plastic surface by suitable adjustment of the concentration of the acid, the noble metal salt and the filler with one another, and the metalized object in this way is used to produce a continuous metal layer on the treated surface a metal using a conventional process is treated.

The plastic object to be coated consists, for example, of 0.5-90% by weight, preferably 10-30% by weight, of the metal oxides mentioned and 99.5-10% by weight, preferably 90-70% by weight, of one polymeric resin.
In principle, all thermoplastics, thermosetting resins and elastomers and mixtures of these resins are suitable as polymeric resins.
Details and explanations of the polymeric resins to be used can be found in U.S. Patent No. 4,590,115. What has been mentioned there also applies to the present invention.

The following resins are preferably used according to the invention: epoxy and acrylate resins, polyimides, polyamides, polyesters, polyurethanes, polyacetals, polycarbonates, melamine resins, polytetrafluoroethylenes, polyvinylfluorides, polyethylenes, polypropylenes, ABS, polyphenylene sulfide, polyetherimides, polyarylene ether ketones, PVC, melamine-formaldehyde resins .

Of the metal oxides, Cu₂O is preferred.

The metal oxides are incorporated into the resin by known methods. Again, details of this can be found in the aforementioned U.S. Patent No. 4,590,115. To ensure uniform noble metal deposition, it is important that the metal oxide is homogeneously distributed in the polymeric substrate. Basically, the polymeric substrates filled with such metal oxides are known and e.g. in U.S. Patent Nos. 3, 146, 125 and 4,590, 115.

The noble metal particles which form in the process according to the invention adhere excellently to the surface of the plastic object to be metallized, and the loss of these noble metals by deposition in the bath is extremely small.

According to the invention, aqueous solutions which contain at least 10 mol / l of a noble metal salt are particularly suitable; the upper limit is not critical and is determined solely by the solubility of the precious metal salts. The preferred concentration range is between 0.01 and 100 g / liter, most preferably between 0.1 and 1 g / liter. The deposited precious metal particles have a typical thickness of less than 1 µm and are distributed discontinuously on the surface.

Particularly suitable as noble metal salts are salts of Au, Ag, Ru, Rh, Pd, Os, Ir or Pt, but in particular salts of Au, Pt or Pd.

Any anions are suitable as anions as long as the salts formed in this way are soluble in an acidic aqueous solution in the concentrations given above.

Suitable salts are e.g. AuBr₃ (HAuBr₄), AuCl₃ (HAuCl₄) or Au₂Cl₆, silver acetate, silver benzoate, AgBrO₃, AgClO₄, AgOCN, AgNO₃, Ag₂SO₄, RuCl₄ · 5H₂O, RhCl₃-H₂O, Rh (NO₃) ₂ · 2H₂O, Rh (CH, COO SO₄) ₃ · 4H₂O, Rh₂ (SO₄) ₃ · 12H₂O, Rh₂ (SO₄) 3 · 15H₂O, PdCl₂, PdCl₂ · 2H₂O, PdSO₄, PdSO₄ · 2H₂O, Pd (CH₃COO) ₂, OsCl₄, OsCl₃, 0OCl₃I 3H₂O IrBr₃ · 4H₂O, IrCl₂, IrCl₄, IrO₂, PtBr₄, H₂PtCl₆ · 6H₂O, PtCl₄, PtCl₃, Pt (SO₄) 2 · 4H₂O or Pt (COCl₂) Cl₂, as well as the corresponding complex salts like NaAuCl₄, (NH₄) ₂PdCl₄, (NH4) , K₂PdCl₆ or kAuCl₄.

Preference is given to those noble metal salts which contain Cl⁻, NO₃⁻, SO₄²⁻ or CH₃COO⁻ as anions and are optionally present in hydrated form.
Particularly preferred noble metal salts are (NH₄) ₂PdCl₆, K₂PdCl₆ and especially PdCl₂, PdSO₄, PtCl₄ and HAuCl₄.

The method according to the invention is particularly simple because the plastic objects to be treated only have to be immersed in the aqueous acidic solution of the noble metal salt without special stirring devices. Alternatively, the aqueous acidic solution can be applied using standard coating technology, such as spraying, brushing or roller coating. The metallization takes place regardless of the shape of the plastic object at all points that come into contact with the solution. However, it can also be expedient to keep the solution in motion during the metallization process. This is done in a manner known per se by shaking or preferably by stirring, e.g. by means of a magnetic stirrer, by moving the sample or by blowing in air.

The temperature of the bath is generally not critical. The metallization is preferably carried out at approximately 10-95 ° C., in particular at a slightly elevated temperature, approximately at 20-50 ° C.

The metallization takes place in an acidic solution. The acidity of the acidic solution also depends on the metal oxide filler used and its concentration in the plastic object. It has been shown that the optimum lies in a relatively low acidity range with regard to the acid concentration.

The acid concentration is adjusted in the usual way using strong acids, such as mineral acids, carboxylic acids or sulfonic acids. Examples include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid or p-toluenesulfonic acid. Phosphoric acid, hydrochloric acid, nitric acid and sulfuric acid are preferred. The concentration of the acid expediently transfers e.g. 0.05 to 90% by volume, preferably 0.1 to 10% by volume.

According to the invention, the concentrations of the acid, the noble metal salt and the filler (metal oxide) are adjusted to one another in such a way that the noble metal is deposited discontinuously and in a sufficient amount so that a complete metal coating is then carried out without any problems (ie with sufficient adhesion and complete coating of the object to be treated). Surface can be obtained.
If, for example, a high acid and noble metal salt concentration is used, it is advisable to use a low filler concentration. When using a high acid concentration and a low noble metal salt concentration, a high filler concentration is expediently used. If, on the other hand, a low acid and noble metal salt concentration is used, it is advisable to use a medium to low filler concentration.
Metallization baths in which the acid and the noble metal salt have the same anion are particularly preferred.

The duration of the metallization naturally depends on various parameters, such as temperature, acid concentration, concentration of the noble metal salt and the filler and, if appropriate, movement of the metallization solution. Typical metallizations usually occur between 10 seconds and 60 minutes, mostly between 30 seconds and 10 minutes.

After the discontinuous metallization step according to the invention, the plastic objects obtained are completely completed in a manner known per se by electrochemical, electrolytic or electrochemical plus electrolytic metal deposition coated. With this layer structure, any metal, for example tin, zinc, cadmium or in particular copper or nickel, can be applied in one step or in several steps carried out separately.

In comparison to the process according to EP patent application No. 0417037, according to which a continuous noble metal coating is produced, the present process allows a perfect metallization of plastic objects of any shape and with excellent application properties, in particular excellent adhesion, although the surface of the plastic Object is only partially and discontinuously metallized with the precious metal. In addition, significantly smaller amounts of precious metal salts are deposited on the surface of the object; this method is therefore less expensive.
According to the present method, it is also possible to adjust the amount of the noble metal particles deposited on the article surface independently of the reduced amount of Cu₂O on the article surface: for example, by treating the plastic article in a solution rich in noble metal salts However, it is low in acid, more precious metal particles are produced than reduced copper parts, whereas fewer precious metal particles than copper parts can be deposited in a solution bath which is low in acid with respect to precious metal salts.
Due to the fact that the metallization according to the invention is discontinuous on the surface of the object, the electrical resistance is infinite. The plastic objects coated in this way are used in a wide variety of industries where metallic surfaces are required, for example in the automotive industry, such as for frames for display instruments, radios, door handles for window regulators, heating grills, dashboard heads, headlights, taillights, etc., also in the radio, TV and electronics industry, in particular for printed circuits, both in multilayer and hybrid circuits and as chip carriers, and in EMI shielding installations, in addition in the aerospace industry, in the dental and medical industry, in the optical industry, for example in the manufacture of mirrors, as well as in household items.

Example 1:

Starting from a laminating resin mixture based on bisphenol A diglycidyl ether with an epoxy content of 2.03 eq / kg, dissolved in methyl ethyl ketone, containing
67.39 parts of laminating resin
2.37 parts hardener (dicyandiamide and 2-methylimidazole; 10: 1)
25, 16 parts of Cu₂O and 5.09 parts of antimony trioxide are suspended therein. This suspension is used to impregnate type 7628 (200 g / m²) glass fabric (manufacturer. Clark-Schwebel). These prepregs are dried and pressed into sheets in 7 layers, the composition of which is as follows: Resin / hardener 38.5% by weight Glass fabric 45.9% by weight Sb₂O₃ 1.3% by weight Cu₂O 14.3% by weight

The resin-rich surface is roughened with emery paper. The plates treated in this way are immersed for 10 minutes at 21 ° C. in an aqueous PdCl₂ solution with a concentration of 0.1 g / l and containing 50 ml / l HCl (37%). The bath is then magnetically stirred at 400 rpm. touched. The plates are then cleaned (rinsed) with water and metallized for 30 minutes at 40 ° C. in a conventional copper bath EC 580 (supplier kemifar). The metal layer thus obtained completely covers the surface of the plastic article and has a thickness of 2.5 microns.

Examples 2-17 :

Reaction conditions and starting materials are analogous to Example 1, but the following parameters or metallization conditions are varied according to the following table.

Example 18:

A polyurethane layer containing 30% by weight of Cu₂O is applied to one side of a molded polyurethane part by in-mold coating. The molded part is treated for 30 minutes at 60-65 ° C in a degreasing bath (Kemifar EC 4035, 10 vol.%). After rinsing with water, the sample is surface-etched for 20 minutes at room temperature in an etching bath (150 ml Kemifar Enplate MLB 497B, 30 ml Kemifar Enplate MLB 497C, 80 g potassium permanganate, 40 g sodium hydroxide, made up to 1 liter with water), the solution is stirred with a magnetic stirrer (400 rpm). After rinsing with water, the manganese dioxide deposited on the surface is removed by immersion for 3 minutes in a 0.1 molar aqueous hydroxylamine sulfate solution under the influence of ultrasound. The molding is rinsed again and then metallized by immersion in an aqueous solution of PdCl₂ (0.1 g / l) containing 100 ml / l HCl 37% g for 6 minutes at 21 ° C. The bath is stirred with a magnetic stirrer (400 rpm). The sample is then rinsed with water and metallized in an EC 580 copper bath for 20 minutes at 40 ° C. The sample is then rinsed with water and coated with copper in a galvano-copper bath (65 min at 28 ° C with 3A / dm²; Kemifar KHT 482). During the electrolysis, the sample is agitated and air is blown into the solution. The copper layer obtained in this way has a layer thickness of 41 microns. The adhesion after the metallization is greater than 6 N / cm. After three weeks of storage, it is greater than 10 N / cm. The side of the molded part that does not contain Cu₂O is not metallized.

Example 19:

Harz/Härter

59,5 Gew.-%

Glasgewebe

39,9 Gew.-%

Cu₂O

0,6 Gew.-%

Starting from a laminating resin mixture based on bisphenol A diglycidyl ether with an epoxy content of 2.03 eq / kg, dissolved in methyl ethyl ketone, containing
96 parts of laminating resin
3 parts hardener (dicyandiamide and 2-methylimidazole; 10: 1)
1 part of Cu₂O are suspended therein. Glass suspension (manufacturer: Clark-Schwebel) of type 7628 (200 g / m²) is impregnated with this suspension in the usual way. These prepregs are dried and pressed into sheets in 7 layers, the composition of which is as follows:

Resin / hardener

59.5% by weight

Glass fabric

39.9% by weight

Cu₂O

0.6% by weight

The resin-rich surface is roughened with emery paper. The plates treated in this way are immersed for 10 minutes at 45 ° C. in an aqueous PdCl₂ solution with a concentration of 0.5 g / l and containing 0.9 ml / l HCl (37% o-ig). The bath is then magnetically stirred at 400 rpm. touched. The plates are then cleaned (rinsed) with water and metallized for 30 minutes at 40 ° C. in a conventional copper bath EC 580 (Kemifar). The metal layer thus obtained completely covers the surface of the plastic object.

Example 20 :

A sample prepared according to Example 1 is treated in stages as follows:
Sources in a copper bath "MLB conditioner 212" (Shipley):
MLB 212: 350ml
Cuposit Z: 35ml
Water: 615 ml
Temp.: 62 ° C
Duration: 5 min.
Magnetic stirrer. 200 rpm;
Rinsing with water;
Etching with kMnO₄ in the following copper bath:
MLB 497B (Kemifar): 150 ml
MLB 497C (Kemifar): 30 ml
KMnO₄: 80 g
NaOH: 40 g
Water. 1000 ml
Temp.: 85 ° C
Duration. 30 min.
Magnetic stirrer. 700 rpm
Rinsing with water;
Deoxidation in an aqueous hydroxylamine sulfate solution (0.1 molar) for 3 min at RT with an ultrasonic stirrer;
Rinsing with water;
Treatment with palladium in an aqueous bath:
PdCl₂: 0.1 g / l
HCl (37%): 100 ml / l
Temp .: 21 ° C
Duration: 10 min.
Rinsing with water;
Copper coating in the EC 580 bath at 40 ° C and for 20 minutes with air blowing;
Rinse with water:
Electrolytic copper treatment in a bath KHT 482 (Kemifar) at 28 ° C for 55 min with 3 A / dm² while stirring the bath and moving the sample;
Rinse with water, then usual air drying and then drying in an oven at 140 ° C for 1 hour.
The thickness of the metal coating thus obtained is 38 microns and the adhesion of the copper is 20 N / cm.

Example 21:

Starting from a laminating resin mixture based on bisphenol A diglycidyl ether with an epoxy content of 2.03 eq / kg, dissolved in methyl ethyl ketone, containing
67.39 parts of laminating resin
2.37 parts hardener (dicyandiamide and 2-methylimidazole; 10: 1)
25.16 parts of SnO and 5.09 parts of antimony trioxide are suspended therein. This suspension is used to impregnate type 7628 (200 g / m²) glass fabric (manufacturer. Clark-Schwebel). These prepregs are dried and pressed into sheets in 7 layers, the composition of which is as follows: Resin / hardener 28.5% by weight Glass fabric 45.9% by weight Sb₂O₃ 1.3% by weight SnO 14.3% by weight

The resin-rich surface is roughened with emery paper. The plates treated in this way are immersed for 10 minutes at 21 ° C. in an aqueous PdCl₂ solution with a concentration of 0.1 g / l and containing 2 ml / l HCl (37%). The bath is then magnetically stirred at 400 rpm. touched. The plates are then cleaned (rinsed) with water and metallized for 30 minutes at 40 ° C. in a conventional copper bath EC 580 (supplier kemifar). The metal layer thus obtained completely covers the surface of the plastic article and has a thickness of 2.5 microns.

Claims (11)

Process for the partial and discontinuous metallization of a plastic article with precious metal particles, according to which the plastic article containing a finely divided, homogeneously distributed filler selected from the group consisting of MnO, NiO, Cu₂O, SnO and Bi₂O₃ is treated with an acidic aqueous solution of a noble metal salt that noble metal particles are partially and discontinuously electrochemically applied to the plastic surface by suitable adjustment of the concentration of the acid, the noble metal salt and the filler to one another, and the thus metallized article is treated with a metal by a conventional method to produce a continuous metal layer on the treated surface becomes. A method according to claim 1, wherein the plastic article consists of 0.5-90% by weight of the filler and 99.5-10% by weight of a polymeric resin. A method according to claim 2, wherein the plastic article consists of 10-30% by weight of the filler and 90-70% by weight of a polymeric resin. A method according to claim 1, wherein the aqueous solution contains at least 10⁻⁵ mol / l of a noble metal salt. A method according to claim 1, wherein the noble metal salt is a salt of Au, Ag, Ru, Rh, Pd, Os, Ir or Pt. A method according to claim 1, wherein the noble metal salt contains Cl⁻, NO₃⁻, SO₄²- or CH₃COO⁻ as an anion. A method according to claim 1, wherein the plastic article is immersed in an acidic, aqueous solution of a noble metal salt or the metallization is carried out by means of a standard coating technology. A method according to claim 7, wherein the metallization is carried out at a temperature of about 10-95 ° C. A method according to claim 1, wherein the acid concentration of the noble metal salt solution is between 0.05 and 90 vol.%. A method according to claim 1, wherein the plastic article obtained is treated after the discontinuous metallization by electrochemical, electrolytic or electrochemical plus electrolytic metal deposition. The plastic object obtainable by the method according to claim 1.