Process for metallizing nonconductive plastic surfaces
The present invention relates to a process for metallizing nonconductive plastics using etching solutions free of hexavalent chromium. The etching solutions are based on permanganate solutions. After the treatment of the plastics with the etching solutions, the plastics are metallized by means of known processes.
1. Process for metallizing electrically nonconductive plastic surfaces of articles, comprising the process steps of:
A) treating the plastic surface with etching solutions to etch the plastic surface, wherein process step A) comprises the following steps, in any order:
treating the plastic surface with an acidic etching solution, and
treating the plastic surface with an alkaline etching solution;
B) treating the etched plastic surface with a solution of a colloid or of a compound of a metal to activate the plastic surface; and
C) metallizing the activated plastic surface with a metallizing solution;
wherein each of the etching solutions comprise a source for permanganate ions.
2. Process according to claim 1 , wherein process step A) comprises the following steps in order:
A i) treating the plastic surface with the acidic etching solution, and
A ii) treating the plastic surface with the alkaline etching solution.
3. Process according to claim 2 , wherein process step A) is preceded by performance of the following further process step:
pretreatment step: treating the plastic surface in an aqueous solution comprising at least one glycol compound.
4. Process according to claim 3 , wherein the at least one glycol compound is selected from compounds of the general formula (I)
wherein
n is an integer from 1 to 4; and
R 1 and R 2 are each independently —H, —CH 3 , —CH 2 —CH 3 , —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 3 , —CH 2 —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 2 —CH 3 , —CH 2 —CH(CH 3 )—CH 3 , —CH 2 —CH 2 —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 2 —CH 2 —CH 3 , —CH 2 —CH(CH 3 )—CH 2 —CH 3 , —CH 2 —CH 2 —CH(CH 3 )—CH 3 , —CH(CH 2 —CH 3 )—CH 2 —CH 3 , —CH 2 —CH(CH 2 —CH 3 )—CH 3 , —CO—CH 3 , —CO—CH 2 —CH 3 , —CO—CH 2 —CH 2 —CH 3 , —CO—CH(CH 3 )—CH 3 , —CO—CH(CH 3 )—CH 2 —CH 3 , —CO—CH 2 —CH(CH 3 )—CH 3 , —CO—CH 2 —CH 2 —CH 2 —CH 3 .
5. Process according to claim 2 , wherein the following further process step is performed between process steps A) and B):
A iii) treating the plastic surface in a solution comprising a reducing agent for manganese dioxide.
6. Process according to claim 2 , wherein the following further process step is performed between process steps B) and C):
B i) treating the plastic surfaces in a conversion solution.
7. Process according to claim 1 , wherein process step A) is preceded by performance of the following further process step:
pretreatment step: treating the plastic surface in an aqueous solution comprising at least one glycol compound.
8. Process according to claim 7 , wherein the at least one glycol compound is selected from compounds of the general formula (I)
wherein
n is an integer from 1 to 4; and
R 1 and R 2 are each independently —H, —CH 3 , —CH 2 —CH 3 , —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 3 , —CH 2 —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 2 —CH 3 , —CH 2 —CH(CH 3 )—CH 3 , —CH 2 —CH 2 —CH 2 —CH 2 —CH 3 , —CH(CH 3 )—CH 2 —CH 2 —CH 3 , —CH 2 —CH(CH 3 )—CH 2 —CH 3 , —CH 2 —CH 2 —CH(CH 3 )—CH 3 , —CH(CH 2 —CH 3 )—CH 2 —CH 3 , —CH 2 —CH(CH 2 —CH 3 )—CH 3 , —CO—CH 3 , —CO—CH 2 —CH 3 , —CO—CH 2 —CH 2 —CH 3 , —CO—CH(CH 3 )—CH 3 , —CO—CH(CH 3 )—CH 2 —CH 3 , —CO—CH 2 —CH(CH 3 )—CH 3 , —CO—CH 2 —CH 2 —CH 2 —CH 3 .
9. Process according to claim 7 , wherein the following further process step is performed between process steps A) and B):
A iii) treating the plastic surface in a solution comprising a reducing agent for manganese dioxide.
10. Process according to claim 7 , wherein the following further process step is performed between process steps B) and C):
B i) treating the plastic surfaces in a conversion solution.
11. Process according to claim 1 , wherein the source for permanganate ions in the etching solutions in process step A) is selected independently from the group of alkali metal permanganates comprising potassium permanganate and sodium permanganate.
12. Process according to claim 11 , wherein the source for permanganate ions in the etching solutions in process step A) is independently present in a concentration between 30 g/l and 250 g/l.
13. Process according to claim 1 , wherein the acidic etching solution in process step A) further comprises an inorganic acid.
14. Process according to claim 13 , wherein the inorganic acid is present in the acidic etching solution in process step A) in a concentration of 0.02-0.6 mol/l based on a monobasic acid.
15. Process according to claim 1 , wherein the alkaline etching solution in process step A) further comprises a hydroxide ion source.
16. Process according to claim 15 , wherein the hydroxide ion source is present in the alkaline etching solution in process step A) in a concentration between 1 g/l and 100 g/l.
17. Process according to claim 1 , wherein the plastic surface has been manufactured from at least one electrically nonconductive plastic and the at least one electrically nonconductive plastic is selected from an acrylonitrile-butadiene-styrene copolymer, a polyamide, a polycarbonate and a mixture of an acrylonitrile-butadiene-styrene copolymer with at least one further polymer.
18. Process according to claim 1 , wherein the following further process step is performed between process steps A) and B):
A iii) treating the plastic surface in a solution comprising a reducing agent for manganese dioxide.
19. Process according to claim 18 , wherein the reducing agent for manganese dioxide is selected from hydroxylammonium sulphate, hydroxylammonium chloride and hydrogen peroxide.
20. Process according to claim 1 , wherein the following further process step is performed between process steps B) and C):
B i) treating the plastic surfaces in a conversion solution to deposit metal ions on the activated plastic surface.