CA1255620A - Process for electrodepositing composite nickel layers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An improved process for producing a composite nickel-containing electroplate on a substrate including an inner nickel-containing layer, of an average sulfur content of less than about 0.03 percent by weight, an intermediate nickel-containing layer of an average sulfur content of about 0.05 to about 0.5 percent by weight and an adjacent adherent outer nickel layer of an average sulfur content of about 0.02 to about 0.15 percent but less in sulfur than the intermediate layer and higher in sulfur than the inner layer. The controlled amount of sulfur is introduced into at least the intermediate layer by employing an aqueous acidic nickel solution containing a controlled amount of a thiazole and/or thiazoline additive compound so as to provide an intermediate nickel-containing deposit containing the specified average sulfur content.

Description

Bac~kground of the Invention The present invention relates to an improved process for electrodepositing a composite nickel containing electroplate on a corrosion susceptible base metal to achieve corrosion protection thereof. The composi-te electroplate com-prises three adjacent, bonded nickel~containing layers each of a controlled thickness and controlled sulfur content which normally are provided with a conventional chrome plate over the surface of the outer nickel layer achieving exceptional outdoor corrosion protection of the basis metal in comparison to a single or even a duplex nickel-containing electroplate of the same thickness.
Composite nickel-containing electroplates are in widespread commercial use for protecting basis metals such as steel, copper,.brass, aluminum or zinc die castings which are subject to outdoor exposure during service, particularly, to marine and automotive service conditions. Beneficial results in corrosion protection are also achieved in the use of such composite nickel-containing layers on plastic substrates which have been subjected to a suitable pretreatment in accordance with well-known techniques to provide an electrically conductive coating thereof such as a copper layer rendering the plastic substrate receptive to nickel electropla-ting. Typical of such plastic materials which can be electroplated are A~S, polyolefin, polyvinyl chloride, and phenol formaldehyde polymers. Such composite nickel-containing electroplates when used in connection with plastic substrates substantially reduce or eliminate so-called "green" corrosion stains produced by a corrosive attack on a copper basis layer or flash.
Typical of such prior art ccmposite nickel-containing ....
electroplating processes and compositions are those disclosed in United States Patent Nos. 3,090,733 and 3,703,448. In accordance with U.S. Patent No. 3,090,733 issued May 21, 1963 a process is disclosed for electrodeposlting a three-layered nickel~containing deposit on a substrate in which at least the operating bath for applying the intermediate nickel layer contains selected sulfur compounds to effect a controlled sul-fur content in the intermediate nickel~containing layer to achieve the requisite adherence between the composite layers and corrosion protection of the underlying substrate. A
further improvemen-t in the foregoing process is disclosed in United States Patent No. 3,703,448 issued November 21, 1972 in which alternative sulfur compounds comprising thiosulfo-nates of nitriles or amides are employed at least in the ope-rating bath for electrodepositing the intermediate layer.
The process of the present invention provides for still further improvements over the compositions and processes disclosed in the aforementioned two patents employing novel sulfur compounds at least in the operating bath for electrode-positing the intermRdiate layer which provides for impro~.~ed bath stability in the presence of air agitation, high tempera-ture and low pH providing for increased plating speeds and reduced consumption of the additive compound. The sulfur ad-ditive compound of this invention provides the further advan-tage in that it can readily be analyzed in the operating bath to maintain its concentration within the opt.imum operating range and in that contamination of the operating bath for applying the outer nickel-containing layer with the sulfur additive co~pound by drag-in frcm the intermediate layer ope-rating bath does not appreciably affect the sulfur concentra-tion of the outer nickel-containing layer. This latter advan-tage is important because normally a water rinse step is not employed between the intermediate and outer nickel plating steps and an undesirable increase in sulfur content of the outer nickel layer can in some instances interfere with cove-rage of the final chromium electrodeposit.
Summary of the Invention The benefits and advantages of the present invention are achieved in accordance with the composition aspects thereof by providing an electrolyte comprising an aqueous acidic solution containing nickel ions present in an amount sufficient to deposit an intermediate nickel-containing layer and a thia-zole compound and/or a tAiazoline compound present in an f V

a~o~nt to prcvide a sulfur content in t~e deposit~d inte~ediate nic~el-containing layer of a~out 0.05 to a~out 0.5 percent æ.
of t~e s~-uc~ural for~Nlae:

X-R ~D < ~ X-R

~' N

Wherein:

X is S, NH;
R is H, R';
R' is -(CH2)n,-503~1, ~(CH2)n C2 n is an integer from 1 to 4;
Y is -503~i ~1 is Na, K, NH4, H
as well as nNL~tures there~f.

In order to attain a sulfur concentration in the lnter~ediate layer within the range hereina~ove s~ecified, the thiazole ccmpound and/or thiazoline c~mpound are typically present in an amount of a~out 0.01 to about 0.4 gr~ms per liter (g/l) with amounts of a~out 0.03 to akout 0.1 g/l ~eing preferred. Ihe inter.~ediate operating bath ~ay also optionally and preferably contain wetting agents and buffering agents such as koric acid, for e~2mple.

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In accordance with the process aspects of the present invention, a metal substrate, or a plastic substrate the sur-face of which has been rendered electrically conductive, is electroplated to form an inner nickel-containing layer gene-rally of a thickness of about 0.15 to about 1.5 mils (3.8 -38 ~) containing an average sulfur concen-tration of less than about 0.03 percent followed by the electrodeposition of an interme-diate nickel-containing layer at a thickness of about 0.005 to about 0.2 mils (0.1 - 5 ,u) and a sulfur content of about 0.05 to about 0.5 percent followed by an outer nickel~containing layer of a thickness genererally about 0.2 to about 1.5 mils (5 - 38 ,u) and a sulfur content of about 0.02 to about 0.15 percent The sulfur concentration of the outer nickel layer is less than that of the intermediate layer but is greater than that of the inner layer which may be substantially sulfur free. Typically, each of the three nickel-containing layers can be ele~trodeposited from a Watts-type nickel plating bath with the intermediate and outer operating baths containing the thiazole and/or thiazoline additive ccmpound in concentra-tions sufficient to deposit the requisite sulfur content in the respective layers. The individual operating baths general-ly are operated within a temperature of about room temperature (20C)up to about 85C and in the case of acidic operating baths, within a p~ range of about 1 to 6.
Additional benefits and advantages of the present in-vention will become apparent upon a reading of the Description of the Preferred Embodiments taken in conjunction with the specific examples provided.

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~escription of the Preferred Embodirnents The cornposite nickel-containlng electroplate can be produced ernploying electrolytes of the types disclosed in United States Paten~ 3,090,733 and 3,703,448, ~Jith the exception that in at least the intermediate operating bath, the sulfur cornpound comprises the thiazole and/or thia~oline ccmpound or derivatives thereof of the specific types hereinafter to be described. Accordingly, the elec-trolyte for depositing the inner nickel layer may comprise a Watts-type nickel plating bath, a fluoroborate, a high chloride, a sulfamate nickel plating bath or a substan-tially sulfur-free semi-bright nickel plating baLh of the types heretofore known. The electrolyte for depositing the intermediate nickel-containing layer may be of the same type ernployed for depositing the inner nickel-contain-ing layer but further containing the thiazole and/or thia-zoline additive compound in approprlate amounts to achieve the re~uisite sulfur content in the intermediate layer.
Similarly, the electrolyte for depositing the outer nickel-containing layer may be similar to that employed for the intermediate layer with -the exception that the concentra-tion of the thiazole and/or thiazoline compound or alter-native sulfur-containing cornpounds will be controlled to provide a net sulfur content in the outer layer in an amount less than that of the intermediate layer. When a decorative plating finish is desired, the outer nickel-containing layer is preferably produced from a bright nickel :.~

plating bath employing one or more of the organic sulfo-oxygen compounds such as set forth in Table II of United States Patent No. 2,512,280 and Table II of United States Patent No. 2,800,440 which compo~nds are also preferably used with unsaturated compounds or amines to give both leveling and brilliance. The three nickel-containing electrolytes may also contain optional components of the types conventionally employed including bath soluble and compatible wetting agents to prevent pitting, buffering agents such as boric acid, formic acid, citric acid, acetic acid, fluoboric acid, or the like.
An electrolyte suitable for depositing the inner nickel containing layer comprises a Watts-type -bath containing about 200 to about 400 g/l nickel sulfate hexahydrate, about 30 to about 100 g/l nickel chloride hexahydrate, and about 30 to about 60 g/l boric acid as a buffering agent. The bath can be operated at a temperature of about room temperature t20C) up to about 85C at a pH of about 1 to about 6.
The intermediate high sulfur nickel-containing layer can be deposited from an electrolyte as employed for the inner nickel-containing layer but further containing from about 0.01 to about 0.4 g/l and preferably from about 0.03 to about 0.1 g/l of the thizole and/or thiazoline additive compound of the structural formulae:

3 ~S~

,~X~ X-II

Y N

Wherein:
X is S, NH;
R is H, R';
Rl is -(CH2)nH~ S03M, (CH2)nC02M;
n is an integer from 1 to 4;
Y is -S03M7 M is Na, K, ~14, H;
as well as mixtures thereof.

Particularly suitable thiazole compounds corresponding to the first structural formula are 2-mercapto thiazole pro-pane sulfonic acid, sodium salt, and 2-amino thiazole propane sulfonic acid, sodium salt. Particularly suitable thiazoline compounds corresponding to the second structural formula hereinbefore set forth are l-amino-5-sulfo thiazoline, sodi~m salt, and 2-mercapto thiazoline.

The specific quantity of the thiazole and~or thiazoline additive compound added to the electrolyte for the interme-diate nickel-containing layer will vary depending upon the specific molecular weight of the compound or mixture of tv compounds employed, the concentration of other constituents present in the electrolyte, the operating parameters under ~hich the bath is operated and the relative concentration of sul~ur in the outer nickel layer to be deposited. Conventionally, the thiazole and/or thiazoline additive compound is controlled so as to provide a sulfur content in the intermediate layer fr~m about 0.05 up to about 0.5 percent by weight, and preferably, about 0.1 to about 0.2%. This sulfur content can usually be attained by employing the thiazole and/or thiazoline additive with amounts of either ccmpound or mLxtures thereof of about 0.03 to about 0.1 g/l usually being preferred.
The outer nickel-containing layer is electrodeposited from an ele~ctrolyte similar to that employed for depositing the inner layer with the exception that the outer layer electrolyte contains appropriate sulfur campounds so as to deposit sulfur in the outer nickel-containing layer within a ranse of about 0.02 to about 0.15 percent by weight. Appropriate sulfur c~mpounds which are preferred are those conventionally ~.,~loyed in bright and satin nicXel baths such as, for example, sodium allyl sulfonate, sodium styrene sulfonate, saccharin, benzene sulfonamide, naphthalene trisulfonic acid, benzene sulfonic acid and the liXe. The thiazole and/or thiazoline additive, benzene sulfinate and thiosulfonates of ni riles or amides are generally not preferred. In any event, the sulfur contPnt in the outer nickel-containing layer is less than that of the intenmediate layer but greater than that of the inner layer. The inner layer ~5~

should have a sulfur content no more than about 0.03 percent by weight, and preferably less than about 0.01 percent by weight.
In accordance with the process aspects of the present invention, the tri-layered composite nickel-containing electrodeposit is sequentially applied usually without an intervening water rinse between successive electrolytes. The composite nickel-containing layer is usually applied to a substrate having a strike of copper, brass, nickel, cobalt or nickel-iron alloy. The inner nickel-containing layer is usually applied in a thickness greater than the outer nickel-containing layer. In order to achieve optimum corrosion protection from the composite electroplate, the ratio of thickness of the inner to the outer nickel-containing layers may range from about 50:S0 up to about 80:20~ The intermediate layer is conventionally applied at a thickness of about 0.005 to about 0.2 mils followed by an outer layer of a thickness of about 0.2 to about 1.5 mils.
In order to achieve optimum atmospheric corrosion protection and decorative appearance, it is usually preferred to apply a final bright conventional chromium plate or a micro-cracked chromium plate or a micro-porous chromium plate of a thickness of about 0.005 to about 0.2 miles over the outer v n~ckel-containing layer. For substrates that are to be ~posed to less severe corrosive conditions during service, the inner and outer nic~el-containing layers may be only about 0.15 mils thick to provide for improved corrosion protection.
It will be appreciated that the nickel-containing layers ccmprising the cGmposite plate may contain other conventional contaminants present in conventional amounts which are introduced into the electrolyte and incorporated in the electrodeposit by way of drag-in or the like. Additionally, cobalt may also be present in the nickel-containing layers in appreciable quantities, such as amounts up to about 50 percent cobalt. For general purposes, however, it has been found preferable that the inner nickel-containing layer be as pure a nickel as possible.
In order to further illustrate the improved composition and process of the present invention, the following examples are provided. It will be understood that the examples are provided by way of illustration and are not intended to be limiting of the scope of the invention as herein described and as set forth in the subjoined claims.

A test solution A comprising a Watts-type nickel plat mg solution is prepared containing about 40 ounces per gallon nickel sulfate hexahydrate, 8 ounces per gallon nickel chloride hexahydrate and 6 ounces per gallon of boric acid.
800 milliliters of test Solution A is added to a 1 liter ~5~

container equipped with nickel anodes and air agitation. The pH of the test solution A is adjusted to 2.5 and the temperature raised to 140F (60C). 75 mg/l of a wetting agent comprising dihe~yl sulfosuccinate is added to the test solution A.
A test solution B is prepared by adding 35 mg/l of 2-mercapto thiazole propane sulfonic acid, sodium salt, to test solution A~ A nickel foil is plated from test solution B and upon chemical analysis is found to contain 0.127 percent sulfur.
The nickel foil is prepared by electrolytically cleaning a two inch by 4 inch steel panel in an alkaline cleaner followed by water rinsing and an acid dip in a 20 percent solution of sulfuric acid. The acid dipped panel is thereafter water rinsed and plated in a Woods nickel strike to provide a nickel strike layer. The resultant panel is passivated by anodically electrolyzing the panel for a period of from one to two seconds in an alXaline cleaner. Thereafter the panel is plated in a test solution B at a current density of 45 ASF for a period of 35 minutes. The panel thereafter is water rinsed, dried and the edges are cut and the resultant nickel foil is removed.

A test solution C is prepared in accordance with the procedure described in Example 1 by adding 50 ms/l of 2-mercapto thiazole propane sulfonic acid, sodium salt, to test solution A. A nickel foil is prepared employing the procedure of Example 1 and upon analysis is found to contain 0.175 percent sulfur.

, . . .

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E~LE 3 A test solution D is prepared by adding 35 mg/1 of

2-~no-5-sulfo thiazoline, sodium salt, to test solution A and a nickel foil is prepared employing the procedure as described in E~ample 1. A chemical analysis of the sul~r content of the foil reveals a concentration of 0.150 percent.

E~LE 4 A test solution E is prepare~ by adding 50 mg/l of 2-amino-5-sulfo thiazoline, sodium salt, to test solution A and a nickel foil is prepared employing the procedure as described in E~le l. A chemical analysis of the sulfur content of the foil reveals a concer.tration of 0.201 percent sul,'ur.

EX~IPT.F~ 5 A test solution F is prepared by adding 35 mg/1 of 2 amino thiazole propane sulfonic acid, sodium salt, to test solution A and a niekel foil is prepared employing the procedure as deseribed in Example 1. A ehemieal analysis of the sulfur eontent of the foil reveals a concentration of 0.l32 percent sulfur.

~ ~PLE 6 A test solution G is prepared by adding 50 mg/l of 2-amino thiazole propane sulfonic acid, sodium salt, to test solution A and a nickel foil is prepared employing the procedure as described in Example 1. A chemical analysis of the sulfur content of the foil reveals a concentration of 0.178 percent sulfur.

EXAMær~ 7 A test solution H is prepared by adding lr) mg/l of 2-mercapto thiazoline to test solution A and a nickel foil is prepared employing the procedure as descri~ed in EXample 1. A
chemical analysis of the sulfur content of the foil reveals a concentration of 0.139 percent sulfur.

EY~LE 8 A test solution I is prepared by adding 20 mg/l of 2-mercapto thiazoline to test solution A and a nickel foil is prepared employing the procedure as described ln Example 1. A
chemical analysis of the sulflr content of the foil reveals a concentration of 0.305 percent sulfur.

E~IPT,F~ 9 A test -solution C as descri~ed in EXample 2 is prepared and used under the conditions described in Example 1 for plating a 1.25 by 6 mch steel panel rolled at one end to prcduce an extremely low ~urrent density area. me plating of the panel is conducted at 30 amperes per square foot IASF) for a period of 7 minutes. The resulting nickel deposit is of a sei~i-bright lustre with good coverage over the low to high current denslty areas.
The test solutions B through I as described in the foregoing examples are eminently satisfactory for use as ar.
electrolyte for depositing the nickel-containing intermediate layer to provide a sulfur concentration within the desired range .
,, _ _ . _ , , , _ , 5~

of about 0.05 to about 0.3 percent by weight. The thiazole and/or thiazoline additive ccmpound provides not only the advantage of improved stability of the electrolyte and high speed plating rates but additionally does not appreciably affect the performance and sulfur content of the outer nickel-containing layer as a result o~ drag-in of the intermediate layer electrolyte into the outer layer electrol~te. It has ~een discovered that when using such thiazole and/or thiazoline additive ccmpounds, less sulfur is deposited with an increase in pH~ Accordingly, the operation of the intermediate layer electrolyte at a pH of about 2.5 provides satisfactory sulfur content in the intermediate layer. However, drag-in of t~e additive into the bright nickel electrolyte for depositing the outer nickel-containing layer which typically is at a pH of about 3.5 to about 4.5 does not appreciably raise the sulfur content of the bright nickel outer deposit.

A series of test solutions designated as J, K and L is prepared by the addition to test solution A of Example 1, 25 ~g/l, 50 mg/l and 100 mg/l, respectively, of 2-~ercapto thiazoline of a molecular weight of 119.2.
A brass appearance panel and a nickel foil are plated from each of test solutions J, K and L at a temperature of about 135 to about 145F at a pH of 2.5 in the presence of air agitation with each solution containing 75 mg/l of the wetting agent dihexyl sulfosuccinate. The 1 by 6 inch brass appearance p2nel is first electrolytically cleaned in an aIkaline cleaner, rolled at one end to create a lcw current density area, ~7ater rinsed, acid dipped in a 20 percent sulfuric acid solution, water rinsed and thereafter plated in the test solution at about 40 ASF for a period of 5 minutes. The appearance panel is thereafter unrolled and the overall deposit evaluated for appearance in khe high and 1c~7 current density areas as ~7ell as for adhesion of ~he deposit. me nickel foils prepared as described in Example 1 are also analyzed for percent sulfur content.
Subsequent analysis and observation revealed a nickel foil containir.g 0.348 percent sulfur produced by test solution J, a sulfur content of 0.396 in the nicXel foil produced by test solution K and a sulfur content of 0.848 percent in the foil prc~uced e~ploying test solution L. It is apparent that the use of this additive ccmpound at the sa~e general molecular concentrations as the ccmpounds previously described in the foregoing ex2mples results in an appreciable increase in the sulfur content of the nicXel layer above that normally desired to achieve satisfactory adherence of the overlying outer nicXel layer of the ccmposite plate. Nevertheless, the general appearance of the panel was satisfactory and adhesion ~as acceptable. Accordingly, the concentration of 2-mercapto thiazoline is preferably contr~lled at concentrations less than about 60 ng/l in accordance with the compositions of test solukions H and I of Examples 7 and 8 to provide an intermediate ~ .

nickel layer containing the desired amount of sulfur.
While it will be apparent that the preferr~d embodi~ents of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjomed claims.

Claims (9)

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

1. In a process for electrodepositing a composite three-layered nickel-containing layer on a substrate wherein an inner nickel-containing layer having an average sulfur content of less than about 0.03 percent by weight is electro-deposited on the substrate, an adherent intermediate nickel-containing layer having an average sulfur content from about 0.05 to about 0.5 percent by weight is electrodeposited on said inner layer and an outer adherent nickel-containing layer having an average sulfur content of from about 0.02 to about 0.15 percent by weight is electrodeposited on said inter-mediate layer and, wherein, said outer layer contains a lower average sulfur content than said intermediate layer and a higher average sulfur content than said inner layer, the impro-vement which comprises electrodepositing said intermediate layer from an aqueous acidic solution having a pH of 1-6 and containing nickel ions in an amount sufficient to deposit the desired intermediate nickel-containing layer and a thiazole and/or thiazoline additive compound present in an amount sufficient to provide the desired sulfur content in the depo-sited intermediate nickel-containing layer, said thiazole and/
or thiazoline additive compounds having the structural formulae:

AND Wherein:
X is S, NH;
R is H, R';
R' is -(CH2)nH, -SO3M, -(CH2)nCO2M;
n is an integer from 1 to 4;
Y is -SO3M;
M is Na, K, NH4, H;
as well as mixtures thereof.

2. The process as defined in claim 1 in which said additive compound is present in an amount to provide a sulfur content in the deposited intermediate layer of about 0.1 to about 0.2 percent by weight.

3. The process as defined in claim 1 wherein said additive compound is 2-mercapto thiazole propane sulfonic acid and salts thereof.

4. The process as defined in claim 1 wherein said additive compound is 2-amino-5-sulfo thiazoline and salts thereof.

5. The process as defined in claim 1 wherein said additive compound is 2-amino thiazole propane sulfonic acid and salts thereof.

6. The process as defined in claim 1 wherein said additive compound is 2-mercapto thiazoline and salts thereof.

7. The process as defined in claim 1 in which said additive compound is present in an amount of about 0.01 to about 0.4 g/l.

8. The process as defined in claim 1 in which said additive compound is present in an amount of about 0.03 to about 0.1 g/l.

9. The process as claimed in claim 1 wherein said inner layer has a thickness of from about 3.8 to about 38 µ, said intermediate layer has a thickness of from about 0.1 to about 5 µ and said outer layer has a thickness of from about 5 to about 38 µ.