An Electrolytic Treatment Device for Preparing Plastic Parts to be Metallized and a Method for Etching Plastic Parts

Abstract

The present invention refers to an electrolytic treatment device having an anodic compartment comprising a non-chromium (VI) etching solution to be treated and immersed therein an anode. The anodic compartment is separated by a membrane from a cathodic compartment comprising a cathodic solution comprising an inorganic acid, wherein the anode and the cathode are used comprising or consisting of a ternary or higher Pb alloy with Sn and at least one further metal selected from the group consisting of Sb, Ag, Co, Bi and combinations thereof. Moreover, a method for etching plastic parts is provided as well.

Claims

1. An electrolytic treatment device having an anodic compartment comprising a chromium (VI) free etching solution as anolyte and immersed therein an anode, a cathodic compartment comprising a cathodic solution comprising an inorganic acid as catholyte and immersed therein a cathode, a membrane separating the anodic from the cathodic compartment; wherein the anode, and optionally the cathode, consist(s) of a ternary or higher Pb alloy with Sn and at least one further metal selected from the group consisting of Sb, Ag, Co, Bi, and combinations thereof, wherein the chromium (VI) free etching solution consists of: 47-74 wt % of at least one inorganic acid, 0.01-5 wt % of at least one periodate salt, 0.01-0.5 wt % of at least one manganese salt, 0.01-5 wt % of at least one iodate salt, and water up to 100%.

2. The device according to claim 1, wherein the at least one further metal is Sb, Bi or Ag.

3. The device according to claim 1, wherein the alloy comprises from 85 to 95 wt. % of Pb.

4. The device according to claim 1, wherein the alloy comprises from 0.5 to 10 wt. % of Sn.

5. The device according to claim 1, wherein the alloy comprises from 0.05 to 10 wt. % of the third metal.

6. The device according to claim 1, wherein the etching solution consists of: 47-74 wt % of at least one inorganic acid, 1-4 wt % of at least one periodate salt, 0.01-0.1 wt % of at least one manganese salt, 0.01-2 wt % of at least one iodate salt, and water up to 100%.

7. The device according to claim 6, wherein the inorganic acid of the anolyte and/or the catholyte is phosphoric acid or sulfuric acid.

8. Method for etching plastic parts with the following steps: a) providing the electrolytic treatment device of claim 1, b) immersing a plastic part in the etching solution as anolyte in the anodic compartment chamber, and c) applying a current from 1 to 8 A/dm.sup.2 for re-oxidising the iodate to periodate in the anodic compartment.

9. The method of claim 8, wherein the temperature during step c) is from 50 to 80° C.

10. The method according to claim 8, wherein the re-oxidation rate to re-oxidize the iodate to metaperiodate is from 0.1 to 1 g/Ah.

11. The method according to claim 8, wherein the dissolution of the anode immersed in the etching solution without any current applied is from 0.1 to 3 g/dm.sup.2 day.

12. The method according to claim 8, wherein the dissolution of the anode immersed in the etching solution with a current from 0.8 to 1 A/dm.sup.2 current applied continuously is from 0.05 to 0.8 g/dm.sup.2 day.

13. (canceled)

14. The device according to claim 6, wherein the etching solution consists of: 47-74 wt % of at least one inorganic acid, 2.2-3.8 wt %, of at least one periodate salt, 0.01-0.06 wt %, of at least one manganese salt, 0.01-0.64 wt %, of at least one iodate salt, and water up to 100%.

15. The device according to claim 6, wherein the periodate salt comprises sodium metaperiodate.

16. The device according to claim 6, wherein the iodate salt comprises sodium iodate.

Description

[0050] FIG. 1 shows different anodes after different exposition into re-oxidation conditions and with different operating conditions:

[0051] A) Pb91 Sb2 Sn7 anode as raw material, before use

[0052] B) Pb91 Sb2 Sn7 anode after immersion in etching anolyte applying 3 A/dm.sup.2 for 10 hours during workday and 0 A/dm.sup.2 for 14 hours during pause at night

[0053] C) Pb91 Sb2 Sn7 anode after immersion in etching anolyte applying 3 A/dm.sup.2 for 10 hours during workday and 1 A/dm.sup.2 for 14 hours during pause at night

[0054] D) Pb90 Sn10 anode after immersion with 3 A/dm.sup.2 during workday and 0 A/dm.sup.2 during pause at night

[0055] FIG. 2 shows a HPLC chromatogram used for the measurement of the concentration of iodate and periodate. The retention peak for iodate can be observed on the chromatogram at 2.5 minutes and the retention peak for periodate at 5.1 minutes.

EXAMPLES

Preparation of the Etching Bath

[0056] The etching bath is prepared with the compounds found in the following table 1.

TABLE-US-00001 TABLE 1 Concentration Compounds Concentration range KMnO.sub.4 0.03 wt % 0.01-0.06 wt % NalO.sub.4 3.20 wt % 2.2-3.8 wt % Phosphoric acid 85% .sub. 67 wt % 54.0-74.0 wt % NalO.sub.3  0.6 wt % 0-0.64 wt % H2O Up to 100 wt % Up to 100 wt %

[0057] The bath temperature should be maintained around 60 to 70° C.

Use of the Anode

[0058] The anodes and cathodes are immersed respectively in the anodic and cathodic compartment and connected to the rectifier. The electrolytic treatment device is powered on at 3 A/dm.sup.2 and the anolyte is circulating from the etching tank to the anodic compartment at 4 L/min flow. Different compositions of anodes were used during those tests and they are listed in table 2 below. Some of the anodes are presented on FIG. 1.

TABLE-US-00002 TABLE 2 Anode Anode Reoxidation surface composition rate Dissolution cleaning Pb Continuous 0.9 g/dm.sup.2 day Not (99.9) 0.2 g/Ah over High dissolution rate necessary Ah applied Thin black powder and problem of bath filtration Pb/Sn From 0.6 to 0 0.04 g/dm.sup.2 day Cleaning (90/10) g/Ah in 60 Ah every 60 Ah Pb/Ca/Sn From 0.6 to 0 0.04 g/dm.sup.2 day Cleaning (98.5/0.05/1.4) g/Ah in 6 h every 60 Ah Pb/Sb Continuous 0.88 g/dm.sup.2 day Not (95/5) 0.5 g/Ah over High dissolution necessary Ah applied Pb/Sn/Sb Continuous 0.22 g/dm.sup.2 day Not (91/7/2) 0.5 g/Ah over necessary Ah applied Pb/Sn/Ag From 0.5 to 0 0.20 g/dm.sup.2 day Cleaning (91/7/2) g/Ah in every 3000 Ah 3000 Ah

[0059] The anode dissolution is measured by the weight loss of the anode over the course of the experiment.

[0060] The re-oxidation rate has been measured by HPLC using a Symmetry C18 4.6×250 mm 5 μm (Waters) column and a detection at 220 nm. The result of such measurement are presented on FIG. 2.

[0061] The results of our test show that we have obtained the best result with the Pb/Sn/Sb anode. They have a good re-oxidation rate with a low dissolution and the lowest maintenance of all the tested anodes.