US 3652351 A
Processes for etching synthetic polymer resins, particularly ABS resins, with aqueous, alkaline solutions of alkali metal manganate (VI) at low temperatures.
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Description (OCR text may contain errors)
United States Patent Guisti  PROCESSES FOR ETCHING SYNTHETIC POLYMER RESINS WITH ALKALINE ALKALI METAL MANGANATE SOLUTIONS Medie B. Gulsti, Spring Valley, Ill.
Cal-us Corporation, La Salle, 11].
May 13, 1970  Inventor:
 References Cited UNITED STATES PATENTS 2,939,772 6/1960 Newman et al ..2 52/79.5
[451 Mar. 28, 1972 3,425,947 2/1969 Rausch et al. ..252/79.5 3,489,625 l/l970 Dell et a1. .,252/79.5
OTHER PUBLICATIONS Zahn et al., Electroplating ABS Graft Polymers," 56(11) 773- 779 1966) of Kunstoffe.
Primary Examiner-Robert F. Burnett Assistant Examiner-R. J. Roche Attorney-Johnston, Root, O'Keeffe, Keil, Thompson & Shurtleff ABSTRACT Processes for etching synthetic polymer resins, particularly ABS resins, with aqueous, alkaline solutions of alkali metal manganate (VI) at low temperatures.
3 Claims, No Drawings INTRODUCTION Synthetic polymer resins, such as acrylonitrile-butadienestyrene interpolymers (ABS plastics), can be prepared for electroless plating with acidic oxidizing systems. These systems have usually consisted of an oxidizing agent, such as chromic acid and a strong acid, such as sulfuric acid. The toxicity of the chromium compounds, their potential hazards as water pollutants, and the fairly high temperatures (55-70 C.) at which these systems are operated have been some of the disadvantages associated with these systems. A system which would produce similar etching of plastic articles made from the synthetic polymer resins but which has fewer of these disadvantages has long been sought.
THE INVENTION It is a principal object of this invention to provide a unique kind of etching pretreatment of plastic objects, particularly those made of electroplatable grades of ABS resins, which are to be first electrolessly and then electrolytically plated.
It is another object of this invention to provide an etching process with a chromium-free, manganate (VI) etching bath at temperatures between 25 and 550 C.
This invention concerns chromium-free etching of synthetic polymer resins, particularly acrylonitrile-butadiene-styrene interpolymers (ABS plastics), at temperatures between about 25 and 555 C. The etching compositions consist essentially of 2.5 to 8.5 percent potassium and/or sodium manganate (Vl), 30 to 70 percent sodium and/or potassium hydroxide, and 2l.567.5 percent water.
The most favorable concentration ranges for these compositions are 40-70 g./l. (4-7%) of the alkali metalmanganate (Vl), 400-600 g./l. (40-60%) of the alkali metal hydroxide, and 230-560 g./l. (23-56%) water, although compositions with concentrations as low as 30 g./l. alkali metal manganate, 300 g./l. alkali metal hydroxide, and 670 g./l. water may demonstrate some etching ability. Temperature ranges for the use of these etching baths are from 25 to 55 C. in general, as the manganate ion concentration increases, the temperature required for etching is lower, and that as both temperature and manganate concentration are increased, the time required for sufficient etching decreases. A five to thirty minute etching period generally is used.
The object of electrolessly depositing a layer of adherent metal on the plastic surface is to provide a base for electrolytic metal plating. Once the electroless deposit is laid, then plating can proceed in much the same way as if a metal were being electroplated.
The usual four steps in electroless plating are conditioning,
sensitizing, activating and chemical plating.
Conditioning prepares the surface to accept and hold a metal deposit. It is sometimes called roughening, and may be accomplished physically (abrasion) or chemically (etching). Usually etching is achieved by soaking in an acidic-oxidizing solution, such as the H SO -CrO etch.
Sensitizing and activating are two steps which accomplish the following: deposit of a thin layer of a tin (II) salt, usually stannous chloride, followed by a dip into a solution containing a noble metal (platinum or palladium salt). The tin is oxidized, and the platinum or palladium is reduced to the metal. The concentration of stannous chloride in the sensitizer is usually about g./l., and the concentration of palladium chloride in the activator is usually between 0.25 and 0.5 g./l. There are various ways to accomplish this end, and different methods and names are used for these two steps, and sometimes they are combined in one step. However, the end result is a fine film of a noble metal which serves as a catalyst for the electroless metal deposition in the final step.
Plating is the final step of the electroless plating procedure. Both copper and nickel have been used. Sometimes a layer of copper is first deposited, followed by a layer of nickel. Copper systems usually consist of copper salts, caustic, other salts, and formaldehyde. Nickel systems usually contain nickel salts and strong reducing agents, such as boranes or hypophosphites.
Water rinses are used between each step to avoid contamination of the baths.
The invention will be further appreciated from the following examples.
EXAMPLE 1 Potassium manganate (V1) is produced in situ by the reaction of potassium permanganate and an alkali metal hydroxide at a temperature of -90 C. Fifty grams of KOH, 5 g. of KMnO and 20 g. of water are mixed and heated to 80-90 C with stirring. The mixture is held at this temperature with stirring until deoxidation reaction is complete, and the solution is bright green. Twenty grams of water are added and the solution is allowed to cool to working temperature. At 40 C., a piece of ABS plastic is etched in this solution for 10 minutes. Satisfactory adhesion of the electroless nickel deposit is achieved.
Adhesion characteristics are judged by several criteria. First a piece of scotch tape was pressed on the freshly electrolessplated plastic and thereafter removed. The tape was then checked to see if any of the metal deposit was pulled off by the pressure sensitive adhesive 'Second, the appearance of the plating is observed to ascertain whether it had a smooth, evenly distributed, glossy finish. Third, the plated plastic was observed under a microscope to check for a fine, smooth grain, even texture and good coverage of the plastic surface by the electroless-plated metal. Fourth, a piece of freshly electroless-plated plastic is scratched in such a way that the plastic substrate formed a curl. The adhesion on the metal deposition to this curl is inspected under the microscope. Finally, by a simple scratch test involving scratching of the electrolessplated metal with a fingernail, adhesion is evaluated as being good if the surface is difiicult or impossible to scratch.
EXAMPLE 2 Forty-five grams of NaOH, 6 gm. of NaMnO and 20 gms. of water are mixed and heated to 8090 C., with stirring, to produce sodium manganate (VI). Twenty-nine grams of water are added, and the solution used as an etchant for ABS plastic at a temperature of 30 C. for 20 minutes. Satisfactory etching is achieved EXAMPLE 3 Twenty-five grams NaOl-l 25 g. of KOH, 2.5 g. of KMnO,, 2.5 g. of NaMnO,, and 20 g. of water are stirred and heated to 8090 C., to produce a mixed manganate (VI) solution. Twenty grams of water are added, and the solution used as an etchant for ABS plastic at a temperature of 30 C. for 20 minutes. Satisfactory etching is achieved.
The aforesaid ABS plastics may be reinforced with fiberglass. Preferably, they are graft polymers or polymer blends of the type described in Us. Pat. No. 3,445,350. The blends contain at least 20 percent by weight of ABS graft polymer, the remainder being polyvinyl chloride, polyurethane, polycarbonates, etc.
It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose of illustrating the invention.
The invention is hereby claimed as follows:
1. A process for pretreatment of an electroplatable synthetic polymer article containing at least 20 percent of an acrylonitrile-butadiene-styrene interpolymer to be electrolessly plated which comprises etching a synthetic polymer surface 3. A process'as claimed in claim 1 wherein said polymer article is made of an electroplatable acrylonitrile-butadienestyrene graft polymer, and wherein said etching solution consists essentially of 4-7 percent potassium manganate (Vl), sodium manganate (Vl), or mixtures thereof, 40-60 percent potassium hydroxide, sodium hydroxide, or mixtures thereof, and 23-56 percent water, said percentages being by weight.
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