Metal plating on plastics

A simple and highly effective process for preparing the surface and plating a plastic or elastomer material is disclosed by the present invention. A uniform, highly adherent metal layer is deposited by the claimed process. The surface of the materials to be plated is prepared by exposure to a gas etch atmosphere and activation of the etched surface by providing a metal colloid thereon. Another aspect relates to the use of a one-step or two-step conditioner treatment in the process for improved results. After the surface preparation and activation, a desired metal coating can be electroless metal plated in a conventional manner.

TECHNICAL FIELD 
The present invention relates to a process for metal plating various 
plastic or elastomeric materials with metals and more particularly, to an 
improvement in the process of preparing the surface of these materials so 
as to provide them with a base or prime coat which will readily accept 
metal plating. 
DESCRIPTION OF THE PRIOR ART 
It is well known in the art that electroplated metal coatings will not bond 
or adhere to plastic or elastomeric materials unless the surfaces of these 
materials are first suitably prepared. A common treatment would include 
etching the plastic with solutions containing chromium trioxide such as 
chromic acid or mixed acid combinations of the chromic/sulfuric or 
chromic/sulfuric/phosphoric types. These strongly oxidizing solutions 
micro-roughen and chemically alter the surface of the plastic materials by 
forming polar organic functional groups such as R--SO.sub.3 --H, 
R--CO.sub.2 --H, and R--CH.dbd.O. The presence of these polar groups 
promotes adsorption of plating catalysts from aqueous solutions which 
allows subsequent metal deposition to readily occur. 
There are two main disadvantages of using solutions containing chromium 
trioxide. First, the concentration of these solutions must be controlled 
within a predetermined narrow range or during the subsequent plating step, 
the plastic surface will either be plated non-uniformly or fully plated 
with a coating of inadequate bond strength. A further disadvantage relates 
to the removal and detoxification of hexavalent chromium compounds from 
these solutions. In an effort to avoid these problems, treating solutions 
based on alternate chemicals have been sought. 
Processes utilizing treating solutions of sulfonating agents have been 
tested as substitutes for chromium trioxide. Initial attempts in this area 
included liquid phase sulfonation using solutions of dilute sulfur 
trioxide in an inert chlorinated solvent, chlorosulfonic acid, 
concentrated sulfuric acid or oleum, and vapor phase sulfonation using 
dilute gaseous sulfur trioxide, chlorosulfonic acid, or fluorosulfonic 
acid in an inert gas. Examples of these processes are found in U.S. Pat. 
Nos. 3,607,350, 3,578,484, 2,945,842, 2,937,066, and 2,854,477. 
A disadvantage of these liquid phase sulfonation solutions is that extreme 
roughening of the surface of the plastic occurs rapidly so that short term 
exposures are required. Also, if the plastic is held in these solutions 
for too long a period of time, it will decompose, char, or carbonize. This 
degradation does not occur when vapor phase sulfonation is used, but, if 
moisture is present, it can combine with the sulfur trioxide to form 
sulfuric acid. This acid condenses on the surface of the plastic and 
prevents uniform conditioning of the entire surface, which after 
subsequent electroplating, results in a nonuniform metal coating. 
An improved sulfonation process for treating or conditioning the surface of 
plastic part for subsequent electroplating can be found in U.S. Pat. No. 
4,039,714, and modifications of this improved process can be found in 
U.S. Pat. No. 4,308,301. The inventions of these patents, however, are 
subjected to the previously described problem of sulfuric acid 
condensation and have a further disadvantage in that a prolonged 
conditioning time produces an unsatisfactory bond strength. 
The aforementioned prior art treatments all relate to the etching step in a 
metal plating process. The remaining process steps include: 
(a) sensitizing the etched surface of the plastic material by immersing the 
plastic into an acidified solution of stannous chloride, 
(b) activating the sentitized surface by immersing it into an ionic 
solution containing a noble metal catalyst to absorb metal nuclei onto the 
surface, and 
(c) electroless metal plating a desired metal onto the noble metal nuclei.

DESCRIPTION OF THE INVENTION 
It is one object of the present invention to provide a simple and highly 
effective process for treating or preparing the surface of any kind of 
plastic or elastomeric material so that the treated surface is able to 
accept a uniform and highly adherent metal coating. 
Another object of the present invention is to provide a new process for 
metal plating plastic or elastomeric materials which utilizes an improved 
surface preparation treatment. 
A further objective is to provide plated plastic or elastomeric articles 
which are coated with a uniform metal layer of high bond strength. 
Other objects of the present invention and advantageous features thereof 
will become apparent as the description proceeds. 
Basically, the process for treating or conditioning the surface of a 
plastic material comprises 
(a) exposing the plastic material to a gas-etch atmosphere containing 
sulfur trioxide or a halogenated sulfonic acid in a inert gas, and 
(b) activating the treated surface by contact with a metal colloid catalyst 
to render the surface receptive to electroless metal deposits. 
Step (a) is known in the art and is represented by U.S. Pat. Nos. 4,308,301 
and 4,039,714, and the content of each of those patents is expressly 
incorporated by reference herein. 
Other gases such as chlorine can at times be advantageously used in 
admixture with sulfur trioxide but in an amount so that the sulfur 
trioxide remains the primary etching gas. 
Another advantage relates to the tolerance of a colloidal metal to humidity 
or moisture in the treating gas without affecting the uniformity of the 
surface conditioning. A practical advantage of this is that ambient air of 
high humidity can be used in the gas etch step to improve the surface etch 
results for subsequent activation with a metal colloid activator. The 
amount of water contained with the treating gas or gas carrier (air) is 
not critical so long as the amount is sufficient to improve the etching 
results. The amount of water present should not be too high so that 
sufficient SO.sub.3 residual gas is left to properly etch the substrate. A 
relative humidity of between 10 to 90% has been found to be satisfactory. 
Satisfactory operating temperatures for this process can range from ambient 
to 275.degree. F., although it is preferably carried out at about 
100.degree.-150.degree. F. 
One of the key inventive features to the improved results of this process 
is the use of colloidal metals to activate the surface of the plastic or 
elastomeric material. The prior art processses utilized either one or 
two-step ionic noble metal catalysts in the activation step. For improved 
results, a sensitizing treatment of immersing the material to be plated 
into a acidified solution of stannous chloride was performed prior to 
activation. In the early stages of development of these processes, 
however, the prior art taught that colloidal noble metals such as 
colloidal palladium should not be used with gaseous sulfonation if a good 
quality electroplated coating was to be obtained on a plastic or 
elastomeric substrate. Surprisingly, in the present invention, the use of 
colloidal metals for activating surfaces treated with gaseous sulfonation 
compounds or similar atmospheres achieves certain benefits over the prior 
art. For example, when using colloidal metals, the degree of etch on the 
plastic can be varied over a much wider range compared with the very 
narrow requirements of etching that is needed when using an ionic 
catalyst. 
A further advantage when using colloidal catalysts also relates to the 
conditioning time. Whereas the prior art teaches that prolonged treatments 
provide poor bond strengths, the present invention finds the opposite; 
that the bond strength of the plated coating is improved with prolonged 
treatments of set conditions of gas concentration, temperature, etc. A 
prolonged treatment for ABS resin, for example, would be 70 seconds at 10 
mole percent SO.sub.3 and 140 seconds at 8.5 mole percent SO.sub.3. 
The etch reaction can thus be regulated or controlled to accept a uniform 
deposit of colloidal catalysts by regulating the SO.sub.3 concentration, 
time of reaction, temperature, humidity conditions, and terminating the 
reaction in the treating chamber by treatment with ammonia, for example. 
Terminating the reaction in the treating chamber is particularly 
advantageous when using high mole percent SO.sub.3 concentrations. The 
regulation and control of the etching step is, in essence, empirical and 
will vary depending on the plastic being employed. The degree of etch can 
be determined by routine experimentation for any plastic that will react 
with SO.sub.3. Thus, applicants have discovered that the surface etch can 
be controlled to subsequently accept a colloidal metal activating agent 
which was previously not thought to be possible. 
Regarding the types of metal colloid catalysts that are useful in the 
activation step of the process of the present invention, noble metals in 
colloid form provide the best results. This would include colloids of 
palladium, platinum, silver or gold, as well as other known noble metals. 
It has also been found, however, that the less expensive, more common, 
transition metal colloid catalysts also provide satisfactory results. This 
category would include copper, nickel, cobalt, and iron. Also, metal oxide 
or metal halide colloids can be used, as can combinations of any of these 
metal, metal oxide, or metal halide colloids. The colloidal metals, 
whether they be elemental, oxides, halides, or mixtures thereof should 
have a sufficiently low valence to cause activation of the plastic surface 
for subsequent electroless deposition. These colloidal metal solutions are 
well known in the art and have been used commercially for many years. If 
the metal colloidal solution is an oxide having a high valence state, 
reduction of the oxide colloid after deposition on the plastic surface may 
be necessary to achieve activation. 
The metal colloids can be used in a one step or two step process and 
plastic parts are immersed into a solution of a metal colloid in a 
conventional manner. Generally, the solution is maintained at about 
70.degree. to 140.degree. F. and preferably at about 
80.degree.-100.degree. F., and the parts are immersed for about 0.5 to 10 
and preferably 1-3 minutes. 
In another aspect of this process, a one or two step conditioner treatment 
is used after the gas etch treatment but before the activation step to 
improve the degree of surface activation by the metal colloids. 
The two step conditioner treatment consists of a first step where the 
material to be plated is immersed into a non-ionic surfactant conditioner 
solution following the gas etch, and a second step, whereby the 
conditioned plastic material is rinsed in an alkaline solution of a pH 9 
or above. The use of this conditioning treatment permits a greater 
proportion of the metal colloid to be adsorbed onto the plastic surface 
than would otherwise occur. The greater the metal colloid included on the 
surface of the etched plastic, the easier it is to initiate metal plating. 
The one step conditioner treatment consists of a solution comprising a 
suitable non-ionic surfactant in an alkaline cleaner described previously. 
In preparation, it is preferred to add the surface active agent to the 
alkaline or acid solution. The alkaline solution can be the same as that 
described below with respect to the two step conditioner treatment. In 
case of the one step conditioner treatment the pH can range between about 
1 and 12. The preferred alkalis to be used are trisodium phosphate and 
sodium carbonate. Hydrochloric acid is the preferred acid. 
These surfactants include any non-ionic surfactants alone or in combination 
in a concentration of from about 0.1 to about 1 weight percent, and 
preferably about 0.2 weight percent. The temperatures and immersion times 
would be the same as for the alkaline cleaner step. The use of the 
conditioners permits additional advantages such as a broader operating 
range of etch, a broader list of permissible plastics that can be treated 
with good results, better adhesion to the plastic surface, and other 
similar improvements. 
The conditioner treatment (one or two step) promotes absorption of the 
catalyst by interacting in some manner with the surface of the etched 
plastic. The present invention utilizes non-ionic polyoxyalkylenes or 
alkyl phenol polyoxyalkylene adduct solutions, such as polyoxyethylenated 
polyoxypropylene glycols and polyoxyethylenated alkylphenol. 
Polyoxyethylene glycol is preferred. The non-ionic sufactants can be used 
alone or in combination with each other. Amphoteric surfactants can also 
be used in combination with the non-ionic surfactants. Aryl containing 
surfactants are best utilized with the one step conditioner treatment, 
alkyl phenol ethoxalates are preferred. A conditioner concentration of 
from about 0.1 to 10 weight percent in a solvent of deionized water can be 
used and 1 weight percent is preferred. The conditioner solution 
temperature can range between 70.degree. and 160.degree. F. and is 
typically about 100.degree. to 130.degree. F. The part to be conditioned 
is immersed into this bath for a period of 0.5 to 10 minutes and 
preferably about 1-2 minutes. 
The alkaline cleaning solution used to rinse the parts after exposure to 
the conditioner solution has a pH of about 9 or above, preferably 11. 
Commercially available alkalis such as sodium or potassium hydroxide, 
sodium or potassium carbonate, trisodium phosphate or the like can be 
used. A solution temperature range of between 70.degree. and 200.degree. 
F. can be used with 125.degree. to 145.degree. F. being preferred. Parts 
are immersed between 0.5 to 10 minutes, and preferably 1 to 2 minutes. 
After cleaning, with or without the use of a conditioner, a neutralizer dip 
is used to remove any residual alkali from the surface of the plastic 
parts. The neutralizers used are typically acid, such as 10 to 30% 
hydrochloric, and they can also include complexing or reducing agents if 
desired. Processing conditions can include a bath temperature of from 
70.degree. to 170.degree. F., preferably 100.degree.-120.degree. F., and 
an immersion time of 0.5 to 5 minutes, preferably 1-2 minutes. When the 
one step conditioner employs acid, neutralization is not necessary. 
However, some acid dip is advantageous to insure removal of the excess 
surfactant from the surface. 
The activation step of the process of the current invention utilizes the 
conventional and known metal colloids described above, and is a surprising 
improvement over the one or two step ionic catalysts of the prior art. 
The accelerator step that follows activation removes any stannous chloride 
or stannous hydroxide from the part surface by treatment in a dilute 
solution of acid or acid salt as is well known in the art. Typically, a 
10% by weight hydrochloric acid solution is used, but chloride or fluoride 
salts, and chlorinated or fluorinated compounds can be added to increase 
the effectiveness of the acceleration process. Usually, this solution is 
maintained between 70.degree. and 165.degree. F. and preferably at about 
110.degree.-120.degree. F. It sometimes is agitated with air, and parts 
are immersed from 5.0 to 5 minutes and preferably about 1 minute. 
Metal plating electrolessly occurs when the activated parts are immersed 
into a solution containing a metal salt, and a reducing agent. Complexing 
agents, stabilizers, and a buffer to control pH are also generally 
employed. Nickel or copper can be autocatalytically deposited onto the 
activated plastic or elastomeric part. The metal colloid on the surface 
acts as a catalyst to initiate deposition after which autocatalytic 
reduction of the metal occurs. A uniform metal film of about 0.25 to 0.5 
.mu.m thick is usually deposited. These electroless plating solutions are 
well known in the art and commercially available. 
The commercially available processes for depositing nickel commonly use 
sodium hypophosphite as the reducing agent. These solutions are generally 
held at between about 70.degree. and 160.degree. F. and preferably at 
between about 90.degree. and 100.degree. F., at an alkaline pH, preferably 
between 8 and 11, and parts are immersed in the solution for 5 to 10 
minutes. The deposit generally contains 2 to 6 percent phosphorus, balance 
nickel. There can be considerable variations in bath formulations, and 
such solutions can contain nickel sulfate, sodium citrate, ammonium 
chloride, ammonium hydroxide, or sodium hydroxide. In addition, 
stabilizers can be added to prevent decomposition of the solution or to 
control the deposition rate. 
Copper deposition processes use formaldehyde as the reducing agent, while 
bath temperatures and exposure time are similar to those for nickel. 
After the initial layer of copper or nickel is deposited, subsequent layers 
of metal can be plated from suitable standard metal electroplating baths 
such as copper, nickel, or chromium. 
Finally, it should be noted that after each step of the process, a thorough 
water wash or rinse is desireable to obtain a successfully deposited metal 
coating. Also, multiple water rinses, where practical, are recommended. 
Electroplating is performed in a conventional manner as is well known in 
the art by placing or suspending the activated plastic material or article 
as the cathode into an electrolyte. The metal to be deposited is used as 
an anode and the electrodes are connected to a current source. The cathode 
current density is adjusted to correspond to the optimum working 
conditions of the electrolyte. 
For the purposes of this invention, metal plating is used to include 
conventional electroplating, as well as the so called "electroless" 
plating processes (i.e.--those processes for metal plating that do not use 
an applied electric current). The most common electroless process is the 
catalyzed chemical reduction method, and this is characterized by the 
selective reduction of metal ions at the surface of a catalyzed substrate 
which is immersed in an aqueous solution. This reduction continues to 
occur onto the substrate through the catalytic action of the deposit 
itself. The advantage of electroless plating over electrolytic 
electroplating is that a dense, virtually non-porous metal coating of 
uniform thickness is provided on all surfaces of the part regardless of 
its shape or geometry. 
The process of the present invention is operable with any plastic or 
elastomeric material that will react with SO.sub.3. Examples of these 
materials are given in U.S. Pat. No. 4,039,714 to Roubal, et al, and are 
expressly incorporated herein by reference. 
The plastic or elastomeric substrate may contain conventional filler 
materials such as glass fibers, asbestos, other mineral fillers, sawdust, 
carbonaceous materials such as graphite, dyestuffs, pigments, etc. 
The plastic carrier for the metal layer may be of different shape such as 
in the form of films, foils, molded articles, rods, fibers, foams, woven 
textile materials, or the like. 
Also, the plated plastic articles of the present invention can be 
subsequently heat treated without adversely affecting the quality of the 
metal coating. In fact, heat treatments usually improve the bond strength 
of these coatings considerably as is well known. 
Finally, the plated plastic or elastomeric articles produced by these metal 
plating processes are characterized by a uniform, dense metal coating that 
is strongly adherent. 
While it is apparent that the invention herein disclosed is well calculated 
to fulfill the objects above stated, it will be appreciated that numerous 
modifications and embodiments may be devised by those skilled in the art, 
and it is intended that the appended claims cover all such modifications 
and embodiments as fall within the true spirit and scope of the present 
invention. 
EXAMPLES 
A further understanding of the present invention, and the advantages 
thereof, can be had by reference to the following examples. 
EXAMPLE 1 
This example demonstrates the beneficial effects of humidity in the 
processing of plastics for plating applications. Also, a colloidal 
palladium/tin catalyst was used in place of an ionic palladium/tin two 
step catalyst. 
The test parts in this example were made of ABS plastic and were to be 
plated for decorative purposes. Two samples were etched as follows: 
Sample 1: 
21/2 minutes, 1 mole percent sulfur trioxide under dry air conditions. 
Sample 2: 
21/2 minutes, 1 mole percent sulfur trioxide under ambient (humid) air 
conditions. 
Both samples were subsequently neutralized with gaseous ammonia, and then 
processed through the following plating cycle: 
(1) Water Rinse 
(2) Alkaline cleaner (sodium carbonate and trisodium phosphate pH=11) for 
21/2 minutes at 130.degree. F. 
(3) Water Rinse 
(4) Neutralizer dip (30% hydrochloric acid) 
(5) Colloidal palladium/tin catalyst for 21/2 minutes at 100.degree. F. 
(palladium concentration 30 ppm). 
(6) Water Rinse 
(7) Accelerator (10% hydrochloric acid) for 11/2 minutes at 125.degree. F. 
(8) Water Rinse 
(9) Electroless nickel bath for 7 minutes at 80.degree. F. 
(10) Water Rinse 
(11) Copper Plate 
(12) Nickel Plate 
(13) Chrome Plate 
The results obtained are tabulated in Table 1, and show that humidity in 
the gas etching step results in more uniform, better adherent coatings. 
TABLE 1 
______________________________________ 
Sample 
Item 1 2 
______________________________________ 
Etch Condition Dry Air Humid Air 
Coverage 80% 100% 
Adhesion Poor Good 
(blistered coating) 
Rack plating None None 
______________________________________ 
EXAMPLE 2 
The parts of Example 1 were also processed using a different catalyst 
concentration (step 5) and different accelerator conditions (step 7) as 
follows: 
(5) Colloidal palladium/tin catalyst for 21/2 minutes at 100.degree. F. 
(palladium concentration=40 ppm) 
(7) Accelerator (10% hydrochloric acid) for 21/2 minutes at 120.degree. F. 
Upon plating those parts, the following results were obtained. 
TABLE II 
______________________________________ 
Sample 
Item 1 2 
______________________________________ 
Etch Condition Dry Air Humid Air 
Coverage 90-95% 100% 
Adhesion Good Good 
Rack Plating Yes No 
______________________________________ 
Regarding Examples 1 and 2, it is not obvious that the introduction of 
humidity in the etching step will produce a beneficial effect in terms of 
selectively etching the part surface and not the rack coating when 
preparing of ABS for decorative and/or functional plating. Rack plating 
refers to plating taking place on the plastisol coatings used on plating 
racks as insulation, and it is very undesirable to have any plating take 
place here. 
EXAMPLE 3 
To demonstrate the improvement involved in the use of a conditioner step 
followed by an alkaline cleaner step, the following tests were performed. 
Four samples of impact resistant polystyrene test panels (Styron 484 made 
by Dow Chemical Co.) were etched by exposure for 61/2 minutes to 1 mole 
percent sulfur trioxide under dry air conditions as in Example 1. The 
parts were then neutralized with gaseous ammonia in the etching vessel and 
subsequently treated as follows: 
______________________________________ 
Processing Time For 
Samples (Minutes) 
Step 1 2 3 4 
______________________________________ 
Conditioner (1% Polyoxy- 
-- 1 21/2 
21/2 
ethyleneglycol), 70 F. 
Alkaline cleaner, (sodium 
-- 1 1 -- 
carbonate and trisodium 
phosphate, pH = 11), 130 F. 
Neutralizer (10% hydro- 
-- dip dip dip 
chloric acid), 
Colloidal palladium/tin 
21/2 21/2 21/2 
21/2 
catalyst, 80-85 F. (30 ppm Pd) 
Accelerator (10% acid), 
11/2 11/2 11/2 
11/2 
105-110 F. 
Electroless nickel 
8 8 8 8 
bath, 85 F. 
______________________________________ 
Results are tabulated below in Table III. 
TABLE III 
______________________________________ 
Property 1 2 3 4 
______________________________________ 
Percent Coverage 
5% 100% 100% 100% 
Tape Adhesion -- Fair Good Fails 
(ASTM Test D-3359) 
______________________________________ 
The results of Examples 3 and 4 show that the interaction of a sulfonated 
surface with a one or two step conditioner, will produce a completely 
coated, well adherent metal coating on the plastic. This process also 
works on other types of plastics, such as glass filled polyesters, 
polysulfones, polycarbonates, as well as others, whether in the foam or 
solid state. 
EXAMPLE 4 
To demonstrate the effectiveness of a one-step conditioner treatment, three 
samples of a modified polyphenylene oxide material (Noryl 190, 
manufactured by General Electric Co.) were etched in an atmospheric 
containing 1 mole percent SO.sub.3 under dry air conditions, neutralized 
as in Example 3, and subsequently processed as follows. 
______________________________________ 
Processing Exposure Time 
for Samples (minutes) 
Step 1 2 3 
______________________________________ 
Conditioner (1% polyoxy- 
1 -- -- 
ethylene glycol), 70 F. 
Conditioner (0.2% polyoxy- 
-- -- 1 
ethylene glycol) in 
Alkaline Cleaner, 130 F. 
Alkaline Cleaner (Sodium 
1 1 -- 
carbonate trisodium 
phosphate pH = 11) 
Neutralizer (30% hydro- 
dip dip dip 
chloric acid) 
Colloidal palladium/tin 
2.5 2.5 2.5 
catalyst, 85 F. (30 ppm Pd) 
Accelerator (10% hydro- 
1.5 1.5 1.5 
chloric acid), 105-110 F. 
Electroless Nickel 
10 10 10 
Bath, 85 F. 
______________________________________ 
Results are tabulated in Table IV. 
TABLE IV 
______________________________________ 
Sample 
Property 1 2 3 
______________________________________ 
Percent Coverage 
100 0 100 
Tape Adhesion Excellent -- Excellent 
(ASTM Test B-3359) 
______________________________________ 
EXAMPLE 5 
To demonstrate that exposure of plastics to high sulfur trioxide 
concentrations does not adversely effect the adhesion of the applied 
metallic layer to the plastic substrate, the following test was conducted. 
Five ABS substrates were etched with varying sulfur trioxide concentrations 
as follows: 
______________________________________ 
sulfur trioxide exposure time 
Sample concentration (mole %) 
(seconds) 
______________________________________ 
1 3.3 140 
2 5 140 
3 8.5 140 
4 8.5 70 
5 10 70 
______________________________________ 
The samples were further processed as follows: 
______________________________________ 
Exposure time for Samples (minutes) 
Step 1 2 3 4 5 
______________________________________ 
Colloidal palladium/tin 
2 3 3 6 5 
catalyst 
Accelerator 1 1 3 1 10 (seconds) 
(10% hydro- 
chloric acid) 
Electroless nickel bath 
6 6 6 6 6 
______________________________________ 
After processing, the sample was electroplated with copper and the adhesion 
of the coating was measured. Results are below in Table IV. 
TABLE V 
______________________________________ 
Sample 
1 2 3 4 5 
______________________________________ 
Adhesion 4 4 8 4 8 
(lbs/in) 
______________________________________ 
EXAMPLE 6 
In contrast to the above, ionic palladium used in solutions as a two step 
catalyzation process produces a result which varies in adhesion in a more 
dramatic way compared with the colloidal palladium/tin catalyzation 
procedure on sulfonated surfaces of ABS. For example, five ABS samples 
were sulfonated by exposure to sulfur trioxide gas and one half of each 
sample was analyzed to determine the surface concentration of sulfur 
resulting from the reaction of the polymer and sulfur trioxide gas. The 
remaining half of the panel was exposed to a two step ionic tin, ionic 
palladium catalyzation process followed by electroless nickel and a 25 
micron copper electrodeposit. The pull adhesion as measured according to 
ASTM-B-533 was correlated to the degree of sulfonation, and the results 
are listed in Table VI. 
TABLE VI 
______________________________________ 
Peel Strength 
Sulfur Conc. 
Sample Pounds/in. mg/cm.sup.2 
______________________________________ 
Unetched 0 2 
1 2 7 
2 7.0 12 
3 7.5 14 
4 7.3 16 
5 2 39 
______________________________________ 
Sample 5 in Table IV corresponds to Sample 5 in Table V. It is apparent 
that the adhesion values fall more rapidly in the case of processing with 
ionic solution two stage catalyst compared to the colloidal catalyst. 
EXAMPLE 7 
A non-precious metal colloid activating solution can be employed to 
catalyze and promote adhesion of metal to plastic on sulfonated surfaces. 
Accordingly, ABS panels (EP 3510 Cycolac) were treated with sulfur 
trioxide gas at 1 mole percent concentration for 2.5 minutes and 
subsequently exposed to an activating copper colloid. Following this 
exposure, the panel was immersed in an electroless copper solution 
followed by copper electrodeposition. Adhesion tests according to ASTM 
B533 produced 4.5 to 5.5 lbs/inch width adhesion for the plate. 
EXAMPLE 8 
To demonstrate the importance of the conditioner, glass filled polyester 
samples were etched for 21/2 minutes in a 2 mole percent dry sulfur 
trioxide and neutralized with gaseous ammonia in the reaction vessel. The 
four samples were then removed, rinsed in water, and processed. 
The processing time for each sample is given below: 
______________________________________ 
Processing Exposure Time 
for Samples (minutes) 
Step 1 2 3 4 
______________________________________ 
Alkaline Cleaner (sodium 
1 1 1 1 
cargonate and trisodium 
phosphate pH = 11) 130 F. 
Neutralizer (30% hydro- 
1/2 1/2 1/2 1/2 
chloric acid) 70 F. 
Colloidal palladium/tin 
3 10 15 3 
catalyst (palladium 
concentration = 40 ppm) 100 F. 
Accelerator (10% hydro- 
1 1 1 1 
chloric acid) 110 F. 
Electroless nickel bath 
30 30 30 30 
90 F. pH 8.6 
______________________________________ 
Sample 4 was also exposed to a conditioner for 2 minutes at 70.degree. F. 
before being processed according to the steps in the table. 
The results for all samples are given in Table VII. 
TABLE VII 
______________________________________ 
SAMPLE 1 2 3 4 
______________________________________ 
Coverage skips 100% 100% 100% 
Tape Adhesion 
Fails Fails Good Good 
(ASTM test 
B-3359) 
______________________________________ 
It can be seen that, whereas without the conditioner the sample would have 
to stay in the catalyst for 15 minutes in order to obtain acceptable 
results in terms of adhesion and coverage, when the conditioning step is 
included the catalyst residence time can be reduced considerably with 
similar results. 
EXAMPLE 9 
Glass filled polyester samples were etched for 5 minutes in 2 mole percent 
sulfur trioxide gas under humid air conditions, neutralized as in Example 
7, and subsequently processed as follows: 
Samples 1 and 2 were exposed to a catalyst having a palladium concentration 
of 60 ppm, Sample 3 100 ppm and Sample 4 40 ppm. The processing time for 
each sample is given below. 
______________________________________ 
Processing Exposure Time 
for Samples (minutes) 
Step 1 2 3 4 
______________________________________ 
Alkaline Cleaner (sodium 
1 1 1 1 
carbonate and trisodium 
phosphate, pH = 11) (130 F.) 
Neutralizer (10% hydro- 
1/2 1/2 1/2 1/2 
chloric acid) (70 F.) 
Colloidal palladium/tin 
3 5 10 3 
catalyst (100 F.) 
Accelerator (10% hydro- 
1 1 1 1 
chloric acid) (110 F.) 
Electroless nickel bath 
30 30 30 30 
pH = 8.6 (90 F.) 
______________________________________ 
Sample 4 was also exposed to the conditioner for 11/2 minutes before being 
processed according to the steps in the table. 
The results for all samples are given in TABLE VIII: 
TABLE VIII 
______________________________________ 
SAMPLE 1 2 3 4 
______________________________________ 
Coverage 25% 70% 100% 100% 
Adhesion Fails Fails Fails Good 
______________________________________ 
These samples show that the use of the conditioner enables the use of low 
catalyst concentrations and short processing times while still obtaining 
acceptable results (i.e., 100% coverage and good adhesion using the ASTM 
D-3359 tape test.) 
The electroless nickel bath used in the above Examples contained 6 g/l of 
nickel as NiCl.sub.2 .times.6H.sub.2 O, ammonium chloride 30 g/l, ammonium 
citrate 15 g/l, sodium hypophosphate 30 g/l and water.