Pretreatment of plastic surfaces for metallization to improve adhesion

Abstract

The present invention relates to the adhesional pretreatment of plastics surface prior to their metallization by chemical or electrochemical methods and may be used in those industrial fields where decorative or functional metallic coatings on top of the plastic surfaces are needed. The purpose of the proposed invention is a high-quality adhesional pretreatment of plastic surface prior to metallization. The purpose is achieved by treating the plastic before to etch it 5-15 min at 50-70 C. in the alcaline permanganic solution containing 1-3M NaOH and 0.1-0.5 M permanganate ions and acidic permanganic etching solution additionally contains 0.5-8.0 M of copper nitrate and the etching is performed at room temperature during 5-60 min.

Claims

1. A method for pretreatment of a plastic surface for metallization, the method comprising: contacting the plastic surface with a first aqueous solution comprising 1M to 3M NaOH and 0.1 to 0.5 M MnO.sub.4.sup. at a temperature of 50 C. to 70 C.; removing the plastic surface from the first aqueous solution as a treated plastic surface; contacting at room temperature the treated plastic surface with a second aqueous solution comprising an acid, Cu(NO.sub.3).sub.2, and MnO.sub.4.sup. to form an etched plastic surface.

2. The method of claim 1, wherein the Cu(NO.sub.3).sub.2 is present in the second aqueous solution at 0.5 M to 8.0 M.

3. The method of claim 1, wherein the MnO.sub.4.sup. is present in the second aqueous solution at 0.2 M to 0.5 M.

4. The method of claim 1, wherein the MnO.sub.4.sup. is present in the first aqueous solution as KMnO.sub.4.

5. The method of claim 1, wherein the MnO.sub.4.sup. is present in the second aqueous solution as KMnO.sub.4.

6. The method of claim 1 further comprising washing the treated plastic surface with water prior to contacting with the second aqueous solution.

7. The method of claim 1 further comprising washing the etched plastic surface with water.

8. The method of claim 1, wherein the acid is H.sub.3PO.sub.4.

9. The method of claim 8, wherein H.sub.3PO.sub.4 is present in the second aqueous solution at 2M to 6M.

10. The method of claim 1 further comprising contacting the etched plastic surface with a third aqueous solution comprising CuSO.sub.4 to form an activated plastic surface.

11. The method of claim 10, wherein the third aqueous solution comprises about 0.2 M CuSO.sub.4 at a pH of about 6.

12. The method of claim 10 further comprising contacting the activated plastic surface with a fourth aqueous solution comprising Na.sub.2S.

13. The method of claim 12 further comprising contacting the etched plastic surface with a fifth aqueous solution comprising PdCl.sub.2 and HCl.

14. The method of claim 1, wherein the contacting of the plastic surface with the first aqueous solution is conducted for 5 minutes to 15 minutes.

15. The method of claim 1, wherein the contacting at room temperature is conducted for 5 minutes to 60 minutes.

Description

EXAMPLES OF EMBODIMENT

(1) Plastics ABS, PC/ABS, PEI (with glass fibre filling), PEEK (with carbon fibre filling) which have flat surface of at least 14 cm are maintained at 60 C. for 5 minutes in alcaline permanganic solution consisting of 1 M NaOH, 0.4 M KMnO.sub.4, the restwater. Further the plastics are washed under tap water (if they were maintained in alcaline permanganic solution) and are dipped for 5-60 min into acidic permanganic etcher of room temperature consisting of 2-6 M H.sub.3PO.sub.4, 0-8.0M Cu(NO.sub.3).sub.2, 0.2-0.5M KMnO.sub.4, the restwater. After the etching the plastics are activated for 5 minutes at room temperature in the 0.2 M solution of CoSO.sub.4, which is of pH near 6.0, then are washed with water and then are dipped for 0.5 minutes into 0.2 M solution of Na.sub.2S of room temperature. After that the plastics again are washed with water and further are plated with 1-2 mkm thick Ni layer electrolytically in Wat's bath at standard conditions. Or after etching the plastics are activated during 1-2 minutes in room temperature solution containing 0.001 M PdCl.sub.2 and 0.3 ml/L HCl, then are washed with water and maintained 5 minutes in 0.2M NaHPO.sub.2 solution at 50 C. After that the plastics are plated electrolessly (autocatalysis) at 35 C. during 15 min in the solution containing (M): NiSO.sub.40.1; Na citrate0.1; NaHPO.sub.20.2; NH.sub.3to solution's pH 8.8. In order to measure the adhesion of Ni coating deposited electrolessly or electrolytically the Ni coating is further plated with copper electrolytically to reach total thickness 50 mkm in the solution (M): CuSO.sub.41.5; H.sub.2SO.sub.42.0, restwater. To evaluate Ni coating's adhesion to plastic the force needed to peel off 1 cm wide strip of the coating at right angle is measured. Conditions of the plastic's adhesional pretreatment and the values of Ni coating adhesion obtained as a consequence of pretreatment are given in the Table. Effect of ABS advance maintaining in the alcaline permanganic solution and of copper nitrate adding to acidic permanganic etcher on coating's adhesion is seen comparing examples 1, 2, 4. Example 3 is showing that the minimum concentration of Cu(NO.sub.3).sub.2=0.5 M in the etching solution even though less effective, however it still helps to obtain coating's adhesion to ABS adequate for practice. Comparing examples 2 and 5 we can ascertain that the adhesion of Ni coating is independent of the method how Ni coating is obtained. Examples 5 and 6 are testifying that the effectiveness of the etching solution is rising sharply if the increase of Cu(NO.sub.3) in it is considerable even in the case of lower H.sub.3PO.sub.4 concentration. Comparing examples 6 and 7 we note positive influence of maintaining time in the etching solution to the Ni coating's adhesion with ABS. Same law is characteristic for PC/ABS plastic (examples 8-12). In case of PEI and PEEK plastics (examples 13-19) in contrast to ABS and PC/ABS plastics,advance maintaining in an alcaline permanganic solution does not rise adhesion values, thus is not needed. However Ni coating's adhesion values to PEEK are very dependant on the fact, whether the etching solution is containing Cu(NO.sub.3).sub.2 and how much of it (examples 17-19).

(2) TABLE-US-00001 TABLE Alcaline First Ni permanganic layer: solution: electroless Used (+)/ Acidic permanganic Etching (e-less)/ Example Not etchant, (M): time, electrolytic Adhesion, No. Plastic Used () H.sub.3PO.sub.4 CU(NO.sub.3).sub.2 KMnO.sub.4 min. (e-lytic) kN/m 1 ABS 6 0 0.2 10 e-less 0 2 ABS + 6 2 0.2 10 e-less 1.5 3 ABS + 6 0.5 0.2 10 e-less 0.5 4 ABS 6 2 0.2 10 e-less 1.0 5 ABS + 6 2 0.2 10 e-lytic 1.5 6 ABS + 2 7 0.2 10 e-lytic 1.8 7 ABS + 2 7 0.2 5 e-lytic 1.4 8 PC/ABS 6 2 0.2 15 e-lytic 0.4 9 PC/ABS + 6 2 0.2 15 e-lytic 0.6 10 PC/ABS + 2 7 0.2 15 e-lytic 0.7 11 PC/ABS + 6 0 0.2 15 e-lytic 0 12 PC/ABS + 2 7 0.2 5 e-lytic 0.5 13 PEI 2 8 0.5 60 e-lytic 0.8 14 PEI + 2 8 0.5 60 e-lytic 0.8 15 PEI 2 8 0.5 10 e-lytic 0.2 16 PEEK + 2 8 0.5 60 e-less 2.4 17 PEEK 2 8 0.5 60 e-lytic 2.4 18 PEEK 6 0 0.5 60 e-lytic 0 19 PEEK 6 1 0.5 60 e-lytic 0.6