Chromium-free plating-on-plastic etch

Abstract

The present invention relates to a chrome free etch for plating on plastic processes, wherein plastic surfaces are contacted in a first etching step with an etching solution at least comprising Mn(IV)-ions and, in a second etching step, with a solution at least comprising Mn(III)- and Mn(VII)-ions prior to the metal plating step.

Claims

1. Process for metallization of plastic surfaces at least comprising the steps of a) Cleaning, b) Etching, c) Rinsing, d) Activation and e) Metallization, characterized in that etching step b) is a two-stage process, wherein in a first etching step b1) the plastic surfaces are contacted with a first etching solution at least comprising Mn(IV)-ions and, in a second etching step b2), the plastic surfaces are contacted with an etching solution at least comprising Mn(III)- and Mn(VII)-ions; wherein the concentration of the Mn(IV)-ions in the first etching step b1) is ≥0.5 g/l and ≤15 g/l and the concentration of the Mn(III)- and Mn(VII)-ions in the second etching step b2) is ≥0.05 g/l and ≤20 g/l; and wherein the Mn(IV)-ion concentration in etching step b1) and the Mn(III)- and Mn(VII)-ion concentration in etching step b2) is adjusted electrochemically by oxidation of solutions at least comprising one or more Mn(II)-salts.

2. Process according to claim 1, wherein the bath temperature in the first etching step b1) is ≥20° C. and ≤60° C. and bath temperature in the second etching step b2) is ≥30° C. and ≤80° C.

3. Process according to claim 1, wherein the pH of both etchings solutions in the etching steps b1) and b2) is ≤1.0.

4. Process according to claim 1, wherein the etching solutions in step b1) and b2) each at least comprise an acid selected from the group consisting of phosphoric acid, sulfuric acid, methanesulfonic acid or combinations thereof.

5. Process according to claim 1, wherein the bath of etching step b1) further comprises a metal-ion selected from the group consisting of Ag, Bi, Pd, Co or mixtures thereof.

6. Process according to claim 5, wherein the concentration of the further metal-ion in the bath of etching step b1) is ≥50 mg/l and ≤1000 mg/i.

7. Process according to claim 1, wherein the density of the etching baths in etching step b1) and b2) is ≥1.5 g/cm.sup.3 and ≤1.8 g/cm.sup.3.

8. Process according to claim 1, wherein the overall Mn-concentration of the bath in etching step b1) is ≥3.0 g/l and ≤20.0 g/l and in etching step b2) is ≥0.1 g/l and ≤25.0 g/l.

9. Process according to claim 1, wherein the Mn(II)-salt in the baths of etching step b1) and b2) is selected from the group consisting of Mn(II)sulfate, Mn(II)methanesulfonate, Mn(II)methanedisulfonate or mixtures thereof.

10. The process according to claim 1, wherein the first etching solution additionally comprises a stabilizer selected from the group consisting of N′-(2-aminoethyl)ethane-1,2-diamine, dimethyl-bis(oxiran-2-ylmethyl)azanium, hexanedioic acid, chloride or mixtures thereof.

11. The process according to claim 1, wherein the steps are performed in order.

Description

EXAMPLES

(1) 0. Analytical Methods

(2) 0.1 Analytical determination of Mn total

(3) The overall Mn-concentration was accessed by titration with 0.1 m zinc sulfate-solution.

(4) 0.2 Analytical determination of Mn IV+

(5) The Mn IV+ concentration was determined by titration with 0.1 m Fe(III)sulfate-solution or by UV/VIS-calibration curves.

(6) 0.3 Analytical determination of Mn VII+/III+

(7) The Mn IV+ concentration was determined by titration with 0.1 m Fe(III)sulfate-solution or by UV/VIS-calibration curves.

(8) 0.4 Analytical determination: Peeling Test

(9) The peeling test was performed according to DIN 40802.

(10) 0.5 Analytical determination: pull-off-test

(11) The pull-off-test was performed according to DIN EN 4624.

I. Example 1 (Etch According to the Invention)

(12) Prior to the plating on plastic a 2-step etching process is performed, wherein the plastic surfaces are contacted with two different etch solutions. No rinsing step is performed in-between both etching steps.

(13) I.1 Preparation of the First Etching-Solution (for Step b1))

(14) The first etching-solution is prepared using the following composition

(15) TABLE-US-00002 Demineralized water 45 ml/l Mn(II)-sulfate solution 10% 120 ml/l Methansulfonic acid (MSA) 70% 300 ml/l H.sub.3PO.sub.4 85% 60 ml/l H.sub.2SO.sub.4 conc. 550 ml/l Catalyst (Ag-MSA: 275 g/l Ag) 2 ml/l Stabilizer N′-(2-aminoethyl)ethane-1,2-diamine, 0.5 ml/l dimethyl-bis(oxiran-2-ylmethyl)azanium; hexanedioic acid The first etching solution can be characterized by Density 1.659 g/ml pH <0

(16) Before the first etching solution can be used at least a part of the Mn.sup.2+ (0.5-6 g/l) is oxidized to an oxidation state of +IV. This oxidation was performed for 10 h at 2 A/dm.sup.2/l (43° C., cathode stainless steel, anode platinized titanium). It is also possible to use platinized Niob or MOX-anodes. Upon oxidation the solution changed the color from light pink to brownish. In order to maintain the necessary Mn +IV concentration in the bath for repeated etch-treatments a steady state current of 0.5 A/l etch solution may be applied.

(17) The immersion time for the plastic parts in the etching solution 1 was set to 5 minutes.

(18) I.2 Preparation of the Second Etching-Solution (for Step b2))

(19) TABLE-US-00003 Demineralized water 25 ml/l Mn(II)-sulfate solution 10% 60 ml/l MSA 70% 335 ml/l H.sub.3PO.sub.4 85% 55 ml/l H.sub.2SO.sub.4 conc. 470 ml/l The second etching solution can be characterized by Density 1.66 g/ml pH <0

(20) Before the second etching solution can be used at least a part of the Mn.sup.2+ (approx. 1 g/l) is oxidized to an oxidation state of +VII/+III. This oxidation was performed for 6 h at 20 A/dm.sup.2/l (70° C., cathode stainless steel, anode platinized titanium). Upon oxidation the solution changed the color from light pink to purple. In order to maintain the necessary Mn +VII/+III concentration in the bath for repeated etch-treatments a current of 0.5 A/l etch solution may for instance be applied once a week for two hours.

(21) The immersion time for the plastic parts in the etching solution 1 was set to 5 minutes.

(22) I.3 Plating of Parts Etched According to the Invention:

(23) 5 difficult to etch ABS parts were first etched by contacting the parts with etching solution 1 and, without rinsing, with etching solution 2 (as defined above).

(24) The inventively etched plastic parts were plated electrolytically according to the following standard process sequence:

(25) Activation:

(26) quadruple rinse/reducer/double rinse/pre-dip/activator/double rinse

(27) Plating:

(28) accelerator/double rinse/electroless nickel/double rinse/copper dip/rinse/pre-plate copper strike/rinse/bright copper/double rinse/semi-bright nickel/double rinse/bright nickel/double rinse/microporous nickel/double rinse/chromium/double rinse/drying

(29) The resulting deposit was uniform and covered fully the plastic parts without any defects. The adhesion of the deposited layer was determined by a pull-off test and revealed values of at least 10 N/mm.sup.2.

(30) Compared to a standard single step etching process the REM-surface pictures of the inventively plated plastic parts revealed a more uniform plating result. It appears that more butadiene wholes were etched and the etched wholes seem to be homogeneously spread and deeper. In consequence, a better adhesion of the metallic layer is obtained.

(31) Peeling tests were performed on the inventively etched plated plastic parts. The test was performed by 3 independent persons. A defined surface was peeled with a tool and the force which was needed to separate the copper-layer from the plastic was assessed. The result was rated okay if a considerable force has to be applied in order to separate the layers. The adhesion of the double etched parts was considered ok, whereas most of the single etched parts failed (easy delamination). The deposited layers on the double etched plastic were generally free of delaminations and exhibited a good adhesive strength of the metallic layer.

II. Example 2 (According to the Invention)

(32) II.1 Preparation of the First Etching-Solution (for Step b1))

(33) The first etching-solution is prepared using the following composition

(34) TABLE-US-00004 Demineralized water 125 ml/l Mn(II)-sulfate solution 10% 120 ml/l MSA 70% 200 ml/l H.sub.3PO.sub.4 85% 60 ml/l H.sub.2SO.sub.4 conc. 600 ml/l Catalyst (Ag-MSA: 275 g/l Ag) 4 ml/l Stabilizer N′-(2-aminoethyl)ethane-1,2-diamine, 0.5 ml/l dimethyl-bis(oxiran-2-ylmethyl)azanium; hexanedioic acid The first etching solution can be characterized by Density 1.658 g/ml pH <0

(35) Before the first etching solution can be used at least a part of the Mn.sup.2+ (0.5-6 g/l) is oxidized to an oxidation state of +IV. This oxidation was performed for 10 h at 2 A/dm.sup.2/l (43° C., cathode stainless steel, anode platinized titanium). Upon oxidation the solution changed the color from light pink to brownish. In order to maintain the necessary Mn +IV concentration in the bath for repeated etch-treatments a steady state current of 0.5 A/l etch solution may be applied.

(36) II.2 Preparation of the Second Etching-Solution (for Step b2))

(37) TABLE-US-00005 Demineralized water 135 ml/l Mn(II)-sulfate solution 10% 120 ml/l MSA 70% 230 ml/l H.sub.3PO.sub.4 85% 30 ml/l H.sub.2SO.sub.4 conc. 645 ml/l Strong nonionic Fluorosurfactant 0.4 ml/l Triethanolamine 2 ml/l The second etching solution can be characterized by Density 1,675 g/ml pH <0

(38) Before the second etching solution can be used at least a part of the Mn.sup.2+ (approx. 1 g/l) is oxidized to an oxidation state of +VII/+III. This oxidation was performed for 6 h at 0.025 A/dm.sup.2/l (70° C., cathode stainless steel, anode platinized titanium). Upon oxidation the solution changed the color from light pink to purple. In order to maintain the necessary Mn +VII/+III concentration in the bath for repeated etch-treatments a current of 0.5 A/l etch solution may for instance be applied once a week for two hours.

(39) II.3 Plating of Parts Etched According to the Invention:

(40) 5 difficult to etch ABS parts were first etched by contacting the parts with etching solution 1 and, without rinsing, with etching solution 2 (as defined above).

(41) The inventively etched plastic parts were plated electrolytically according to the following standard process sequence:

(42) Activation:

(43) quadruple rinse/reducer/double rinse/pre-dip/activator/double rinse

(44) Plating:

(45) accelerator/double rinse/electroless nickel/double rinse/copper dip/rinse/pre-plate copper strike/rinse/bright copper/double rinse/semi-bright nickel/double rinse/bright nickel/double rinse/microporous nickel/double rinse/chromium/double rinse/drying

(46) The deposited layers are free of delaminations and exhibit a good adhesive strength.

III. Comparative Example—Standard Mn.SUP.3+/7+ Etch

(47) A standard plating-on-plastic was performed on two difficult to etch plastic parts using a single-step etching process. The etching step was performed using the following bath composition:

(48) TABLE-US-00006 DI water 180 ml/l Mn(II)-sulfate solution 10%  60 ml/l MSA 70% 230 ml/l H.sub.3PO.sub.4 85%  30 ml/l H.sub.2SO.sub.4 conc. 645 ml/l

(49) The density of the etching bath was 1.65 g/cm.sup.3 and the etching time was set to 10 minutes. The plating procedure was the same as given above.

(50) The metal plating on the plastic part is very inhomogeneous and the layer is easily peeled of the plastic surface.