CA1203720A - Oxidizing agent for acidic accelerator - Google Patents

Abstract

OXIDIZING AGENT FOR ACIDIC ACCELERATOR

ABSTRACT OF THE DISCLOSURE

A process for treating a polymeric plastic sub-strate to render it receptive to electroless plating in a process of the type including the steps of etching the sub-strate and activating the etched substrate. The present improvement includes the step of accelerating the activated substrate with an improved aqueous accelerating solution con-taining an aqueous soluble compatible oxidizing agent present in an amount effective to increase the activity of the accelera-ting solution. The improved accelerating solution inhibits the plating of stop-off coatings and plating racks and is of versatile use.

Description

OXIDIZING AGENT FOR ACIDIC ACCELERATOR
BACKGROUND OF THE INVENTION
T~is invention relates to a method of treating polymeric substrates to render them receptive to electro-less plating, and more particularly to a method of . . accelerating polymeric substrates using an aqueous soluble oxidizing agent. Reference may also be made to copending Canadian application No. 335,935, filed on December 30, 1981, and entitled "Method of Accelerat-i.ng Polymeric Substrates Using Oxidizing Metal Ions and Alkyl Amines". That application is owned by the same assignee as the present invention and generally relates to the use of an accelerating solution which includes an oxidizing metal ion, a substituted alkyl amine, and a material selected from the group consisting of a mineral acid, an aqueous soluble salt of said sub-stituted alkyl amine, and an aqueous soluble salt of a mineral acid, as well as mixtures thereof.
A variety o~ methods have heretofore been used or propo~ed for use in applying metallic platings to all or portions of the surfaces of polymeric plastic parts.
Such processes conventionally comprise a plurality of se-quential pre-treatment steps to render the plastic substrate receptive to the application of electroless plating wherea~ter the plated part can be processed through conventional electroplating r ~

~2~3~Z~
operations to apply one or a plurality of supplemental metallic platings over all or selected portions oE the pla.stic substrate.
Conventionally, the pre-treatment steps employed include a cleani.ng or series o-f cleaning steps, if necessary, to remove surface Films or con~aminating substances~ Eollowed ~herea-fter by an aqueous acidic e-tching step em-ploying a hexavalent chromium solution to achieve a desired surface roughness or te~ture en-hancing a mechanical interlock between the substrate and the metallic plating to be applied thereover. The etched substrate is subjected to one or a plurality of rinse treatments to extract and remove any residual hexavalent chromium ions on the surfaces of the substrate which may also include a neutralization step including reducing agents to substantially convert any residual hexavalent chromium ions to the trivalent state. The rinsed etched substrate is thereafter typically subjected to an activa-tion treatment, such as in an aqueous acidic solution contain-ing a tin-palladium complex, for example, to form active sites on the surface of the substrate, fol]owed. by one or more rinsing s-teps after which the activated surface is typically subjected to an accelerating ~reatment in an aqueous solution to extTact any residual activator constituents or compo~mds on the surface of the substrate. The accelerated plastic part is again water rinsed and thereafter i.s subjected to an electroless plating operation of any o:E the types knol~n in the art to ap~ly a metallic plate such as copper, nickel, or cobalt over all or certain selected areas thereo-E ~ihereafter the part is rinsed and therea:Eter :is subjected to conventional elec-tro~la-ting o~erations.

-2-~ ~Q

Typical of such plastic plating processes are those described in United States Patents Nos, 3,011,920,

3,532,518; 3,622,370; 3,961,109; 3,962,497; and ~,20~,013, to which reference is made for further details of the processesn The present invention is also applicable to processes of the foregoin~ type and is specifically directed to an improved aqueous accel.era-ting solution which provides benefits and advantages hereto~ore unattainable in accordance with prior art practices.
A continuing problem associated with the electroplating of polymeric substrates has been in ~he careful control of the activation and accelerating steps to achieve a plastic substrate which is receptive to the subsequent electroless plating solution to provide 100% coverage of a conductive metal layer which is adherent to the substrate and which is devoid of any lack of continuity of coverage of "skipping".
The presence of such discontinuities or skips results i.n plastic parts which upon subsequent electroplating contain non-plated areas or non-uniformity in the metallic plating deposit rendering them unsuitable for the :intended end use.
In the commercial decorative plating of ABS or other plastic parts, there are several reasons why it is often desirable that some areas of the plastic surface remain unplated: 1) to enhance the decorative appearance of the part as in the case of decorative painting, 2) for economic reasons as in not wasting valuable metal and pla-ting solutions on areas of the surface that will be invisible when the part is mounted or otherwise incorpora-ted into a final assembly for use' 3) to maintain elec-trically non-conduc-ting areas for insulation, and 4) to maintain non-plated areas for final fastening assembly such as ultrasonic welding of ABS. Prevention of plating is accomplished by selectively coating certain areas of the part with an electrically non-conductive stop-off paint prior to processing the part through electroless metallizing and conventional electroplating. Any of the commercially available stop-off compositions such as Perry & Derrick LECTRO BLOC (trade mark~ 73310 Black Stop-Off Paint, can be employed for this purpose. The formulation of these stop-off paints or coatings is in-tended to be such that they will not be activated and electrolessly metallized in subsequent processing steps.
In practlce, however, lt is often the case that, due to improper use or application, or even due to the chemical composition of~the stop-off coating, c~rtain portions o~
such painted areas will adsorb sufficient activating species to become electrolessly metallized and subsequent-ly covered by the metal layers applied by conventional electroplating techniques. Then the decorative effect, insulating effect, or the economy anticipated is lost and the part is rendered unsuitable for usea --aS~

~37~(~

It is one function of the acidic accelerator used subsequent to the activation step in processing plastic parts for electroless metallization to remove such activating species as may have been adsorbed on stop-off painted areas. However, it has been found that most conventional acidic accélerators -4a-~37~1D

previously available have been somewhat unreliable in this respect. Typically, overplating of the stop-o-f-f coated areas occurs. l~len such acidic accelerators have been operated at high enough concentrations9 long enough irnmersion times, in-creased agitation, or h;gh enough teTnperatures to assure com-plete removal of the activating species adsorbed on stop-of-f coated areas, there has been a very high probability that an excessive amount of activator will also be removed from certain areas of -the exposed plastic on which plating is desired. This results in skips or misplates on these areas, and again the part is rendered unsuitable -for use.
With particular regard to conventional tin-palladium activators, for example, of the type referred to hereinabove9 and which enjoy gre~t popularity today, avoid-ing metal coverage on stop-off coatings hasbeen found to be a problem in view of the varying degrees to which palladium -from the tin-palladium activator is adsorbed on these various coa~-ings. For exalnple, some coatings adsor~ only a small amount of palladium which will subsequen-tly be removed during accelera-tion. However, other coatings adsorb larger amounts of palladiurn which are not removed during subsequent acceleration.
The ob-vious result in the latter case is the undesirable plat-ing of areas coated with s-top-off paint.
I-t shoulcd be noted that polymeric subs-trates ~hich have been acti~ated such as wi-th a tin-palladium complex, for examr)le, are not -ther~arter reacly -for elec-troless pla-ting.
Ille -film formed on the polymeric substrate during i~nersion in the ackivator solutions will not ef-fectively function as a catalyst c~nd induce electroless plating until it is accelerated, which in the case of a tin-palladium activator, for e~ample, is not until the s-tannous chloride also present on the substrate is removed. This is done by "accelerating"
the substrate surface. Acceleration is accomplished by con-tacting the activated polymeric substrate with materials such as mineral acids which catalyze hydrolysis. In the case of a tin-palladil~ activator, for e~ample, it is the hydrolysis of stannous chloride that is catalyzed. Although such treat-ment may also remove a smallamounto the activator constituents such as palladium, a sufficient amount of accelerated residual material remains on the substrate sur-Eace for the subse~uent electroless plating steps.
The possibilities for controlling the activity or strength of most accelerators and thereby overcomi~g undesir-able plating~ as briefly referred to above, include increasing the amount of air agitation used, varying concentration~ con-trolling operating temperature7 or varying the immersion time used. ~lowever, the degree to which these parameters can be varied in a large scale industrial produ~tion installation is limited. This consequently limits the degree of change in activity of the accelerators, and thus limits the efforts to prevent undesired platingr The present invention overcomes these problems by a:llo~ing the activity o~ the accelerator to be varied signi~icc~ntly and therefore overcomes mc~ny o-~ the problems ~, 372~

and disadvantages associated with processes -for the plating Or plas~i.c articles, and pc~rticularly the acceleration thereof, by providing a sol.ution which w;ll inhibit plating on stop-o:E-E paints and plating racks (such as those coated with poly-vinyl chloride or vari.ous plastisols and organisols), and which is of versatile use on a variety of conventional platable plastic materials.

S~ RY OF ~IE INVENTION
The bene-fits and advantages o-f the present inven-tion are achieved by a process in which a polymeric plastic substrate is treated to render it receptive to electroless plating and includes the steps of etching the plastic substrate with an aqueous acid solution containing hexavalent chromium ions and also activating the etched substrate. In accordance with the present inventiont the activated substrate is subse-quently acce]erated with an aq~eous accelerating solution which includes an aqueous soluble compatible oxidizing agent ~resent in an amount ef:fective to increase the activity of the accelerator solution. The accelerated substrate may then be given al~ater rinse maki.ng it ready -Eor conventional electroless plating, which may be followed by one or more conventional electroplating steps. Of course, conventîonal rinsing ste~s may be utilized a-fter the above-re-ferenced etching and activa~ion steps.
It has surprisingly been -found that the use of con-trolled COnceTItratiOnS of oxidizing agents, such as chrorn.ic acid, hyclrogen peroxide, potassi.um iodate, potassilm ~Z(~3~2~

meta-periodate, phosphoric acid, ferric chloride, ferrous chloride, ferrous sulfate, ammonium persulfate, vanadium penta-oxide, or iodine in conventional acidic accelerators is an effective method for making such accelerating solutions sufficiently more aggressive to assure the removal of activat-ing species t~hich have been adsorbed on stop-off painted areas and/or plating racks. For each such oxidizing agent there are ranges or concentrations, which are partially dependent on the operating parameters of other solutions in the processing cycle, within which no overplating of stop-off painted areas or plating racks occurs while yet complete coverage by electroless metalliza-tion of the exposed plastic surfaces is allowed. In any event, the oxidizing agents are used in an ~mount ancl within parameters where the activity of the accelerator solution is increased sufficiently to prevent undesired plating of the type referred to hereinabove.
The process employing the improved accelerating solution of the present invention can generally be performed at concentrations ranging from about 0.1 to about 300 mg/L, of course, as noted a~ove, depending upon the oxidizin~ agent used. Temperatures of from about room temperature up to about 160F are also generally satisfactory, again depending upon the particular oxidizing agent. Time periods of rom about 5 seconds up to about 5 minutes are usually satisfactory, but contact time will vary depending upon tlle type of plastic substrate, the degree of activation thereof, the temperature of thc activat~:ng solution and other related variables. The 372q:~

accelerating solution is generally operated in the acidic range of pH from pl-l=O up to about neutral, but pre-Eerably at a p~l of less than about 1.
Additional benefits and advantages o-f the present invention will become apparent upon a reading of the detailed description of the pre-ferred embodirnents taken in conjunction with the accompanying examples.

DESCRIPTION OF I~ ~REFFRRED FMBOD~NTS
The process of the present invention is applicable for use with any of the various platable plastic or polymeric plastics including acrylonitrile-butadiene-styrene (A~S), poly-aryl ethers, polyphenylene oxide, nylon, and the like. The polylneric plastic parts are usually subjected to a cleaning treatment to remove any surface contamination which may further include an organic solven~ treatment, in some instances, to render the substrate hydrophilic during the subsequent chrome acid etching step. Usually the cleanin~ step is per-forrrled cmploying an aqueous alkali soak solu-tion followed by contact in an organic solvent medium which may co~prise either a single-phase system or an aqueous organic solvent emulsion.
The clean part is thereafter thoroughly ~ater rinsed and is nex~ subjected to an etching treatment in an aqueous acid solution containing hexavalent chromium ions or a mixture of hexava]ent chromium ions and acid, such as sulfuric acid, to e-ffect an etching of ti-e sur-face thereof~ The specific con-centrat-ion of the ctching solution~ the temperature, and the duration oF treatm~nt will vary dependin~ upon the snecific ~;)37~

type o~ plastic substrate and the parameters of the etching step are, accordingly, dictated by procedures well known and practiced in the art.
Following the etching step, the etched poly-meric substrate is subjected to one or more cold waterrinses and may additionally include a neutralization step employing an aqueous solution containing a reducing agent to effect a reduction of any residual contaminating hexavalenl chromium ions to the trivalent state. A
typical neutrali~ation treatment is described in United States Patent No. 3,962,497. Following neutralization, if employed, the substrate is again water rinsed and thereafter is subjected to an activation treatment employing an aqueous acid solution which may contain a tin-palladium complex of the various types well known in the art. A typical one-step activation treatment is described in United States Patent No. 3,011,920 and United States Patent ~o. 3,532,518. Of course, other activator solutions may also be used with the present invention, including those which contain no noble metals or are based on co~on or non-precious metals.
Following the activation treatment, the activated po~ymeric substrate is subjected to one or a series of separate cold water rinse treatments whereafter it is subjected to acceleration in an aqueous solution in accordance with the practice of the present invention as more fully ~w ~ f~

hereinafter to be descrihed. Following acceleration, the par-t is cold water rinsed and thereafter is subjected to an electro-less plating process to at~rly a conductive~ continuous, and adheren~ metallic plate such as copper, nickel, or cobalt over all or selected surface areas thereof. The electroless plating step is perfol-med in accordance with well known and established practices employing an aqueous solution contain-ing a reducing agent and a reducible salt of the metal to be deposited on the surface. Following the electroless plating step, the part is subJected to one or a plurality of water rinse treatments and thereafter can be electroplated by employ-ing normal procedures to apply one or a plurality o:E overlying plate on the polymeric substrate if so desired.
In order to achieve selective plating of only certain areas of polymeric p]astic articles, and as noted above, it is conventional either prior to or following the cleaning step to apply a stop-off coating of the type comtnercially available, to those areas which are not to be plated. The-present invention provides benefits in this regard by achieving proper acceleration of the plastic sub-strate to be plated while inhibiting or substantially completely el~linating plating on such stop-off areas. The present inven-tion also provides similar benefits with regard to ~mdesired plating on plating racks.
The accelerating solution of the present invention compr;ses an aqueous solution containing as its essential con-stit~lent an a~lleous soluble compatible o~idizing agent in an 3~2~
amolmt efEective to increase the activity of the convent:ional accelerating solution, with conventional acidic accelerating solutions such as those based on mineral acids or the like being suitable. The oxiaizing agent added according to the present invention may be further characterized as being compatible witll the activator constituent or the like on the plastic sur-face as well as withthe polymeric material itself. The concen-tration of the oxidizing agent should be chosen so as to be controllable and useful i~ increasing the activity of the acceleration, but yet preventing oxidation of any significant amount oF the activator catalyst or the like on the activated substrate.
Typical of oxidizing agen~s which are suitablefor use in the practice of the present invention are chromic acid, hydrogen peroxide, potassium iodate, potassium meta-periodate, phosphoric acid, ferric chLoride, ferrous chloride, ferrous sulfate, ammonium persulfate, v~n~ Tm pentaoxide, and iodine, as well as mixtures thereof. Typical usable concentration levels, which will be detailed -further hereinbelow, range from about 0.1 to about 300 mg/L. ~or examp:Le, iron III, obtained from such sources as ferric chloride, :Eerrous chloride, and ferrous sulfate (including the addition of hydrogen peroxide and/or air agitation as referred to hereinbelo~), is usable in amo~lts of from about 2 to about 300 mg/L, ~hereas iodine is usable in cuno~mts of :Erom about 1 to about 20 mg/L. Several additional concentration ranges for various materials are given belol~ Of course, ot~ler materials l~ith similar oxidizing prol~erties arc also believed to be usable in accordance with the principles of ~he present invention.
In accordance with a further pre-Eerred embodiment of the present invention, the a~celeratin~ solution may contain a controlled. amo~mt o-f a surfactant to increase uniformity of reaction with -the substrate achieving a more uni-form accelera-tion thereof. Surfactants suitable for use include any of those well kno~l in the art ~hich are compatible wi-th the other bath constituents. Such surfactants, when employed, can be used in amounts of from ab~lt 0.01 up to about 6 g/L.
The accelerating solution ca~ be em~loyed at temperatures ranging -from about room temperature (65F) to temperatures below the boiling point of the solution.
Ordinarily, the accelerating solution is contained in treat-ing tanks incorporating a pro~ective pl.astisol lining and, for practical considerations9 temperatures up to about 160F are employed to avoid any thermal de~radati.on or decomposition of such protective linings. In accordance ~ith a pLeferred practice, the aqueous accelerating solution is e.mployed at temperatures ranging from about 65.to about 160F,which pro-vides for reasonable treating times consistent with the avail-able operating cycle time of the continuous platin~ system.
The aqueous accelerating solution can be applied to the activated plastic substrate by any one of a variety of techniques of which i~nersing the plastic parts in the so.ution constitutes a preferred practice. Generally, immersion times from about 15 seconds up to about 30 minutes can be employed, wllile time per:iods ranging from about 30 seconds up to about 5 miml-tes employing solutions at a temperature of about 65 to about 160F are sat:isfclc~ory for most plastic materials and 72~

part confi~ rati.ons. The specific time period will vary some-what depending upon the nature of the plastic material, the particular oxidizing agent used and its degree o.E activation of the polymeric substrates, as well as the temperature of the solution. Typically, for ABS -type plasti.cs, accelerating treatments of from about 30 seconds to about 90 seconds at temperatures of about 130 to about 150F are satisfactory.
In order to further illustrate the process of the present in~ention, the following examples are provided.
It will be Imderstood that these examples are provided for illustrative purposes and are not intended to be limitin~ of the scope of the invention as herein described and as set forth in the subjoined claims.
EXAMPLFS
A series of test panels of a nominal size of about 3 inches by about 4 inches by 1/10th inch thick, com-prised of a platable ABS plastic were subjected to a pretreat-ment and electroless plating as hereinafter described. The panels were comprised of an ABS plastic commercially available under the desi.gnation PG 299 from ~lonsanto Chemical Company.
After appropriate cleaning, each of the panels was parti.ally coated with Perry ~ Derrick Lectro Bloc 73310 Black Stop-Off Paint w~ich had been thinned 20% by volume ~ith toluene. r~e pane].s were air dried and then oven cured for one hour at a t~mperature o:E about 122F.
The plasti.c pallels were then etched in an aqueolls acid solution corlta;ning 35h g/L chromic acid, 412 ~/L

sulfuric acid, and 0.2 g/L of a perfluorinated proprietary wetting agent commercially available under the designationFC-98 from Minnesota ~lining and ~anufacturing Company. The panels were immersed for a periocl of si~ minutes in the aqueous etching solution main-tained at about 150F while undergoing an air agitation. ~t -the conclusion o-f the etching treat-ment, the panels were removed and cold water rinsed with tap water for a period of about 2 minutes. The rinsed parts were thereafter neutrali~ed in a chromium reducing neutralizer solution containing l~ g/L hydrochloric acid and 3 g/L hydroxyl amine sulfate. ~le neutralization trea~ment was carried out for two minutes with air agitation at a solution temperature of abcut 80F.
After neutraIization, the panels were cold water ].5 rinsed with tap water for about one minute and then were subjected to an activation treatment in an aqueous solution containing 0.077 g/L palladium, 9 g/L tin chloride, 35.2 g/L
hydrochloric acid, and 192 g/L sodi~ chloride. An activation treatment o-f about one minute and 45 seconds at a solution temperature o about 65F was employed. ~lereafter, the panels were cold water rinsed with tap water :for about one minute and then were immersed in an accelerating solution consisting of 96 g/L sodium bisulfate, 20 g/L sodium chloride, and 3 g/L hydroxyl ammonium sulfate, hereinafter referred to as "accelerator A". (Of course, other similar conventional accelerating solutions wi-th similar properties~ including those based on nrinera:L acids or the li~e, may also be suitable in this rcgarcl.) me panels were accelerated for about 2 minutes with air agitation at a temperature of about 140~.
A:Eter acceleration, the parts were again cold water rinsed and subjected to an electroless plating step to apply a nickel plate thereover employing an aqueous bath con-tainin~ 12 g/L nickel chloride hexahydrate [NiC12 ~H2O], 18 g/L of sodium hypophosphite [NaH2PO2 ~2O]~ and 24 g/L citric acid The electroless plating was per-formed at about 65F
for a period of abMJt 6 minutes.
The above procedure resulted in complete coverage of the exposed portion of the ABS panel, and almost complete coverage of that portion of the panel coated with the stop-off paint. In order to prevent and contro:L such t~ldesired plating coverage, the followin~ -further tests were conclucted using the same procedure outlined above, except with the various modi-fica~ions to the accelerating solution rnade in each instance and described hereinbelow:

Example I
The addition of 1 mg/L chromium VI, obtained from an aqueous solution of chromic acid ~CrO3), to accelerator A
resulted in only sl;ght overplate of the stop-of-f paint, while complete electroless nickel coverage was main-tained on the exposed ABS. At 2 mg/L chromium VI, no overplate occurred on the stop-off pain-t, and the exposed ~BS was completely covered l-y elec-troless nickel. No skipping was noted on -the ~BS un-til a concen-tration oE ~ mg/L chromium VI ~as reached.

~3720 Example II

Panels were again prepared and processed as out-lined abo~e. Ho~Yever, in this series of ~ests, it was sho~Yn that the addition oE hydrogen peroxide~ H2O2,to accelerator A
produced no overplate on stop-off paint at a concentration of about 50 mg/L while complete coverage of the exposed ABS was obtained. No skipping on the ABS was obser~ed Ltntil a con-centration of about 100 mg/L H2O2 was reached.

Example III
Panels were prepared and processed as described above except in this case the additi-ve to accelerator A Yas potassium iodateJ KIO3. Good results, i.e.~ no overplate on stop-of paintwitllcomplete coverage of ABS, was obtained between concentTations of 0.2 and 2.0 mg/L. Complete skipping on exposed ABS was not obtained until a concentration of 5 mg/L
KIO3 was reached.

Example IV
Again? panels were prepared and processed as referred -to above, but potassium meta-periodate, KIO~, was added to accelerator A. This produced good results in a con-centration range o-f from about 0.1 to about 1.0 mg/L, and did not procluce skips on A~S until a concentration of 2.5 mg/L Yas reached.

F~YC1mP1e V
Phosplloric acid, l-l3PO~ ias added to accelerator ~L~U~

A in this series of tests, which otherwise followed the pro-cedure described above. ~esults were good between about 100 and 250 mg/L of H3PO~. Severe skips were encol3ntered at 300 mg/L.
Example VI
Panels were prepared and processed as before, except the additive to accelerator A was iron III obtained from an aqueous solution of ferric chloride, FeG13 6H2O.
Upon addition to accelerator A, a portion of the total iron present was reduced to the divalent state by the reducing agent incorporated in the accelerator formulation. Good results were obtained between a total iron concentration of about 50 to 250 mg/L. Above about 300 mg/L, skipping was encountered on the exposed ABS.

Example VII
Additions of ferrous chloride, FeC12 4H2O, were made to accelerator A, and panels were prepared and processed as in the above-referenced procedure. A portion of the total iron present was oxidized by air agitation to the trivalent state. ~lis test yielded good results between total iron concentrations of from about 25 mg/L to about 300 mg/L .
Example VIII
Panels prepared and processed as outlined above were tested witll additions of ferrous sulfate, FeSO4 7H2O, being made to accelerator A. A portion of the total iron present was raised to the trivalent state by air oxidation.
Complete coverage of exposed ABS was maintained without over-plating the stop-off paint from a total iron concentration of from about 15 mg/L to about 150 mg/L.

Example IX
In this series of tests, incremental additions of ~m~nilml persulfate, ~ )2S208, were made to accelerator A
while ABS panels prepared and processed as before were run.
Overplating of the stop-of-f paint was completely eliminated at and above an an~loniwn persulfate concentration of 0.2 g/L.
Only a very slight skip was observed along the stop-off line on the exposed .4BS at a concentration of about 5.0 g/L.

Example X
Incremental additions of v~n~ m pentaoxide, V2O5, were made to accelerator A and ~BS panels prepared and processed as described before were tested. Good results ~rere obtained between a v~n~ lm V concentration of from about 5 mg/L
to about 15 mg/L. Skips were observed on the exposed ABS at a v~n~-lil~ V concentration o-f 20 mg/L.

Example XI
Acldition of 1 mg/L iodine to accelerator A
produced skipping on exposed ABS when panels were prepared and processecl as above with an activa-tor time of 1 min. 45 sec.
llowever, when the ac-tivator time was increased to 4 minutes, no ~2~3~2~

skip~ing was observed until an iodine co-ncentration of 20 mg/L
was reached.
Example XII
Panels prepared c~d plated as detailed above and ~m through an acidic accelerator containing v~n~ ~ V ion as in L~ample X, but with an activator time of ~ minutes, showed no skipping on exposed ABS until a v~n~flil~ V concentration of 35 mg/L was reached. Complete coverage of ABS was restored by decreasing the immersion time in the acidic accelerator from 2 minutes to 30 seconds.
Example XIII
Plastic parts made of the same material as the test panels described hereinabove and having large areas covered by stop-off paint were also prepared and plated in the manner detailed above. Parts treated with accelerator A without any oxidizing agent exhibited serious and persistent overplating on painted areas. Addition of 5 mg/L iron III, obtained from an aqueous solution of ferric chloride, to accelerator A showed an immediate and dramatic decrease in the amount of plating on painted areas. After testing continued for a time, this beneficial effect was seen to disappear. As the iron III removed the activating species from painted areas, it was reduced to the ineffective divalent state. Small in-cremental additions of iron III were continued, and with each addition, the beneicial eEfect was seen to enclure for a longer time. At a total iron concentration oE about 100 mg/L, the condition became sel-~-regillating. Air oxidation produced 37;~

iron III at the same rate that the work load was causing the opposing reduction to iron II. An effective and beneficial level of iron III was thereby automatically maintained in the working solution.

Example XIV
To accelerator A, ferrous chloride, FeC12 4H2O, was added in sufficient quantity to yield an iron II concentra-tion of 150 mg/L. Panels prepared and processed as described hereinabove showed almost complete electroless nickel coverage of the stop-off painted area. One drop of 35% hydrogen peroxide was added to about one liter of the accelerator solu-tion. This oxidized enough of the iron to the trivalent state to eliminate plating on the painted area, but produced skipping on the exposed ABS. Coverage on ABS was restored by decreas-ing immersion time in the accelerator from 2 minutes to 30 seconds.

Example XV
Potassium permanganate, K~lnO4, was tested in the acidic accelerator at concentrations of l, 2, 5, and 10 mg/L, with the remainder of the process being the same as described above. At 1, 2, and 5 mg/L,no beneficial effect was observed.
At 10 mg/L a complete misplate was observed on both the painted area and the exposed ABS. It is concluded from this that the effcctive range for this material is narrow and ~ould be dif:ficult ko control in prac-tice.

~ZC~37ZC~

Example XVI
Additional aqueous accelerating solutions are prepared for use in a process for treating a polymeric plastic substrate to render it receptive to electroless plating~ which process includes the steps of etching the substrate with an aqueous acid solution containing hexavalent chromium ions, activating the etched substrate, and accelerating the activated substrate. The aqueous accelerating solutionsused contain an aqueous soluble compatible oxidizing agent present in an amount effective to increase the activity of the accelerating solution.
Okidizing agents selected from the group referred to and listed above and present ;n an amount of from about 0.1 to about 300 g/L are used. A substrate of the type referred to hereinabove is contacted with the accelerating solution for a period of time of from about 15 seconds to about 30 minutes with the accelerating solution being maintained at a temperature of from ab ~lt 65 to about 160F and a pH of from about 0 to about 7. Upon subsequent electroless plating, reduction or total elimination of plating on electroplating racks and stop-off coatings is observed.

As evidenced by the above-referenced examples, it should be apparent that the use of an improved accelerator solution in accordance with the teaching o-f the present inven-tion provides improved control of the activity of accelerating solutions. A comparison o-F the solutions of exarnples 1 througll 14 and the control solution, ~hich did not contain an oxidizing agent, demonstrates the ability of an oxidizing agent to prevent plating on stop-off paints. In connection with these examples, recluction or ~otal elimination of plating on stop-off paints was observecl.
Among the aclvantages of the present invention in addition to -those described hereinabove, is that by elimin-ating plating on stop-off paint, a cost savings is realized by eliminating metal losses and by eliminating the need to remove the metal plating from the stop-off paint. In addition, un-desired plating on electroplating racks is also preventable utilizing the present invention. Furthermore, the described solutions are of versatile use on a variety of conventional plastic materials.
While it will be apparent that the invention herein disclosed is well calculated to achieve the benefits and aclvan-tages as hereinabove set forth, it will be appreciated that the invention is susceptible to modification~ variation,and change without departing -from the spirit thereof.

-~3-

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for treating a polymeric plastic substrate to render it receptive to electroless plating includ-ing the steps of etching the substrate with an aqueous acid solution containing hexavalent chromium ions, activating the etched substrate, and accelerating the activated substrate, the improvement comprising contacting the activated substrate during the accelerating step with an aqueous accelerating solution containing an aqueous soluble compatible oxidizing agent present in an amount effective to increase the activity of the accelerating solution

2. The process as defined in Claim 1 in which said oxidizing agent comprises a material selected from the group consisting of chromic acid, hydrogen peroxide, potassium iodate, potassium meta-periodate, phosphoric acid, ferric chloride, ferrous chloride, ferrous sulfate, ammonium persulfate, vanadium pentaoxide, and iodine, as well as mixtures thereof.

3. The process as defined in Claim 1 in which said oxidizing agent comprises chromium VI in an amount of from about 1 to about 5 mg/L.

4. The process as defined in Claim 1 in which said oxidizing agent comprises hydrogen peroxide in an amount of from about 50 to about 100 mg/L.

5. The process as defined in Claim 1 in which said oxidizing agent comprises potassium iodate in an amount of from about 0.2 to about 5 mg/L.

6. The process as defined in Claim 1 in which said oxidizing agent comprises potassium meta-periodate in an amount of from about 0.1 to about 2.5 mg/L.

7. The process as defined in Claim 1 in which said oxidizing agent comprises phosphoric acid in an amount of from about 100 to about 300 mg/L.

8. The process as defined in Claim 1 in which said oxidizing agent comprises iron III in an amount of from about 2 to about 300 mg/L.

9. The process as defined in Claim 8 in which said iron III is obtained from a material selected from the group consisting of ferric chloride, ferrous chloride, and ferrous sulfate, as well as mixtures thereof.

10. The process as defined in Claim 1 in which said oxidizing agent comprises ammonium persulfate in an amount of from about 0.2 to about 5.0 g/L.

11. The process as defined in Claim 1 in which said oxidizing agent comprises vanadium V in an amount of from about 5 to about 20 mg/L.

12. The process as defined in Claim 11 in which said vanadium V is obtained from vanadium pentaoxide.

13. The process as defined in Claim 1 in which said oxidizing agent comprises iodine in an amount of from about 1 to about 20 mg/L.

14. The process as defined in Claim 1 in which the substrate is contacted with said accelerating solution for a period of time of from about 15 seconds to about 30 minutes.

15. The process as defined in Claim 1 in which said accelerating solution is maintained at a temperature of from about 65 to about 160°F.

16. The process as defined in Claim 1 in which said accelerating solution has a pH of from about 0 to about 7.

17. The process as defined in Claim 1 in which said accelerating solution further comprises a surfactant present in an amount effective to increase uniformity of reaction.

18. The process as defined in Claim 1 in which said surfactant is present in an amount of from about 0.01 to about 5 g/L.