CA1156965A - Acid zinc plating solutions and method of utilizing ethoxylated/propoxylated polyhydric alcohols - Google Patents

Abstract

Abstract A high quality, bright, and lustrous zinc deposit is obtained from a plating solution consisting of zinc ions, an electrolyte, an organic acid or a salt thereof, and a grain refining agent which is a polyhydric alcohol with three or more hydroxyl groups substituted with one or more oxyalkylene groups.

Description

I ~L569 ACID ZINC rlJATlN~:; SOI~U1ION5 Arlr) Ml T1101) UTIL171N[3 11`i}0XYI.~TEI)/PROPOX~LATI~I) POl,YliYI)RiC Ar,CO~IOLS
DESCRIPlION O~ INV1~N'IION
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1`echr!ict11 Field ' l Tllis inve1ltion rel~t~3s to tbe ficld of el~ctlop1ntinLr, or e]ectrodepositing, 1 2illC and, in pref~rred embodimonts9 to novei ~cicl z:inc plating sol~ltions which flre capuble of providing n higll qlmlity brigllt alld lustrolls æins~ c~eposl~ on a ccnductivc workpiece utilizing conventional electroplating appnratus. The inven-tion ulso provid~s an improved method for elcctroplating high q~lality :zinc coatings from the novel nckl 7inc plating soIutions of the in~ention. Either bright and lustrou.s, or cmi-l)right, zinc platings, Imving excellellt adhesion ~ind a high de~ree Or ductili1y can be produce(l in ~Iccordflncl! witll the invention.
il Bflck~,rc.un(l It is weLl knowll in the nrt thllt brigh~ und lust1ouc: metallic zinc deposits can be electroplated on a m~tullic sllbstrnte from aqllcolls acid ~inc pl~ting solutions, or baths. I-{owever, difficlllties persist in comn~erciaIly producing uniform nnd relinblc zinc co~tings with sl1fficientJy high Ievels o~ brightness and l luster.
¦ For exn1llple, tl~e ternpernturc o~ the plating solution must be controlled ¦ genernlly within a runge o1 abo1lt 60 to 90l- (lr~ to 30C). l'arti~ularly ~t higl1er ten~p~ratu1es, difficllllies f,irc experiencecl with "clou~ling1', or instability of the pIatinLr solutions, particuln1ly Wittl solutioll compollellts which are hydro-phobic or contain hydropliobic substitl1ents. At lower temperutures, difficulties ~ire encotlntere(1 in c~btainirl~ urliform nnd ncceptable ZillC aoatin~s, particlJlally Wi~tl rognr(l to 1lvoi(lllncc of strenl~inLr nn(l lil~e surfrlcc iniperfections.
26 I In convenlionnl aci~1 zinc plnting hnths, 6raill-re1ininLf agents nre utilis~ed ¦I to pro~ oc A com1rlelci~11y aoc(?ptable bright alld lu~trol1~ æin(- coatill~r. Withol1t ~j Lrrnin-l'erillillL'' ~ ,'elitS, the ~:inc contillLr~g prQ~:luce~l t.y convcntion~l b~lhs may not ` 1l exhibit wliformly smooth nnd rerille(l sllr~uces over the full range of currellt densities nol 1nnlly ellcollnterec1 in colllll)erci~l npplicflt1or)s. In the prior art, $~ I

~15~5 grr?ir~refil~in~r rlg~ents llave typicnlly t)een polyctllers which corltflirl substanti~
~i ql~nlltities oî ~ly~lrop~lobic sllb~ itllc?nts, ex~libi~ substrlntial ~;UI tl?ce-nctive pro-perties and nl e clnssified 1S Slll'rnCtUlltS.
1~ I)LIC to lbe presencc of sllbstnlltif~ lfllltities of hy(ll'OpilObiC SllbStitllentS, ¦I the solllbility of thc prior art ~rnin-refirlillg nl~ents in nn ll911eOUS, acid zii~c plnting br?th has been of criticnl importance. Sucll blths typicnlly exl)ibit a low cloud point~, which is the point ~?t Wl?iCh tlle Slll'fnCtnllt or hydrophobic rn~teri~ls !~ begin to separutc from the IqlleollS platillg solutior I It is also desirrlhle to lltilize 6?gitfltion in a Y.inc plnting hath, which is ! typically provided by bubbling nir throllgh tlle platirlg sollltion. Wowever, the ¦ presencc of convention11 gr~?in-refinin~ ngents, wllich nre surfrlctnnts, leads to exce.ss foaming thnt must be colltrolled, nsllnlly by ad(lition Or fulther additives, j such as defonming Igents or tlle liko.
¦Illustrative of nqueous, ncici zinc platin~ systcms utili~ g suc~l prior ~rt igrain-refilling agcnLs are those disclosed in U. S. ~fllenL~ No. 3,92û,528; No.1 3,928,149; No. 4,014,761; No. 4,n75,0r~6; No. 4,119,502; No. '1,137,133; and No.
¦¦ 4,138,394. U. S. Patent No. 3,891,520 discloses use of polyrncrs of polyethylene il glycol, wt)ich nre dihydric alcohols, while U. S. Pntent No. 4~070,256 indicates 11¦ tl~at rlliphntic mollohydric alcohols cnn bc! utilized. flOWeVel-, both the monohydric ! and dihydric fllcollols used in the prior art nrc? surfncc-active agents (i.e., surfactflnts) and are foamers in the acid 7.inc plntin~ bnths in which they rlreutilized. U. S. Patcnt No. 3,9~5,894 discloscs llse of watcr soluble polyglycidols an(3 derivatlves thereof, whicll exhibit poor throwin~ nn~ covering power, nnd l ~n~lse forlnltion Or ~Innccnptabl(! brlrlcl~ or intorforenco in tlle mid-(?llrrent derlsity 1 rnn~es.
In nll of tllec;e nckl %inc plltill~, hnlils ol` lllo plior rll-t, thero remllir?s n j nocd for r? ~rrrlirl-refirlillg n~?nt whicll n-lnkcs littk?, if nlly, (ontriblltion to the I cloud point of lhc bntll, nncl whi(ll (locs not foum in tll~ opernting zinc IIMting I ,solutions.
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~1 ' ~ 3 ~ 65 The improved zinc acid plating solutions and method of the invention provide both a wide latitude of operational utility, particularly with respect to the operable temperatures of the plating bath. They also do not contribute to foaming. They are particularly useful and advantageous because they allow for continuous operation at higher bath temperatures than is presently possible, without deterioration or clouding of the p.ating solutions. In addition, they allow for commercially acceptable plating to proceed at much lower temperatures than is.presently possible. This eliminates the need for preliminary heat up of the plating baths before plating can be started.

SUMMARY OF THE INVENTION
-In accordance with the invention, it has been discovered that aqueous, acid zinc plating solutions for electrodeposition of zinc coatings can be provided substantially entirely free of any content of alkyl naphthyl ethers and alkyl naphthyl ketones and utilizing a grain-refining agent comprising a polyhydric alcohol selected from the group consisting of glycerin having 5 to 30 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 3 to 15 moles of propylene oxide substituted for hydroxyl groups, sorbitol having 6 to 100 moles of ethylene oxide substituted for hydroxyl groups, or sorbitol having 1 to 20 moles of propylene oxide substituted for hydroxyl groups.
Typically, the aqueous, acid zinc plating solutions of the invention contain a source of zinc ions, an electrolyte which provides electrolytically charged ions which are capable of conducting an electric current, at least one organic brightener or luster forming agent, and an organic acid or salt thereof, in addition to the novel grain-refining agents of the invention.
Preferably, these plating solutions also contain a b~lffering agent, as well as other optional additives which do not adversely ~Efect the solubility or stability of the zinc plating solution. 5emi-brigh-t zinc coatings can likewise be produced by variation, elimination, of the amoun-t of brighte.ner userd in these plating solutions.

The plating solutions of the invention can be effectively operated at a temperature ranging from about 50 to 100F (10 to 49C) and at a pH ranging Erom between about 4.5 to 6.5.
I~hese plating solutions effectively have no significant cloud .~

- 3a -: point and substantially no foam is generated by the grain-refining agents of the invention in the plating solution, even when air agitation is utilized.

An improved method for electropla-ting zinc coatings, : 5 preferably having a bright and lustrous appearance, is also provided in accordance with the invention, .............. ~
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5~5 whereby the IIOVel nqueous, rlcicl ~.inc plnting sollltion of tlle invcntion is utili~d for electroplating.
Zinc coatings can be prodllced in nccordance witll the invention wt)ich ¦ exhibit exccllellt grrlin refinement nnd high qllnl~ty bli&rtltllc~ nnd lustcr over Q
S ¦ wide rrlnbre Or currellt densilites nlld l)lnting colls)itions. If less l~rightener is I, used, a semi-bright zinc plate ~aving exccllent ndhcsion and a lligll degree of !¦ duc!tility crln be produced.

i Accordingly, it is fln obj~ct of tl~e irlvcntion to provide improved rlqueous,l ucid zinc plating solutions wl~ich contain grnin-refilling A~ents and permit electro-i deposition of commercially accept~lble bl ibrht nn(l Illstro~ls, or semi-hright, zinc ~ corltin~,s over n widcr range of platirl~r ~onditiolls, mo.st notably tempernture, !~ than is possi~)le ~ith convcntiolllll ncicl ZillC pl~itin"~ bntils.
~, It is rl furtller ol:~ject of the invention to provide ~in improved aqueous, Ii flcid zinc plAt,ng solution which does not foum when nir tlgitation or the like ~. is utiliY.ed (luring electropliting of brigllt and l~l.strous zinc coatin~s.It is yet a f~lrther object of the inven~ion to provide an improved method of electroplntirlg zinc coatings over the widest possible range of plating condltions, I particu]arly temperrlture, and witllout fo~lming.
j~ Other objects ~nd ndvnlltriges of the novcl flqueous, t~cid zinc plating ¦~ solution rlncl Illethod of tl)e invf3ntion will be rendily flppnrent to those skilled in the urt thlou~fll stncly of tlle iollowinFr clescriplion of ~hc.~ preferrcd emhoclirnents ! ~nd the nppen(led clriimY.
l)ESCRIPl~ON O~ PREFERREI) EMBODlMENrlS
ANL~ 5r iUOl)E FOR ARRlilN~, OllT I`l;E INVl~N_ON
2r~ , ~?~ioll o~ f~lr~ l"!)'~ "
An improvc(l ~l911CO~IS, llCi~l XillC' plntillg ,YolUtion Oflp~ble of electroplnting ri~rllt nrl(l luslrolls %Ino co~ltin~ rovicled in tlocordurlce with ~I proferre~l embodill)ent of thQ invf~ntion. Such ~In nql.leolls Qcid ~.inc plntlng bath contnlns n soul-(-e nf zinc iorls in soluliotl. Any convol)i'iollrll sourcc o~ zinc ions c~in be Illilizcd Pol- exnmr"o, zino clllorillc, :~in xlllfnte, zinc sul~mute, zino llcetnte, ' !
j:

zinc fllloboratc ol~ Inixturcs thcrl!of cfln be clissolvecl in aqlleons solutio-l. Never-theless, it is fully within the pllrview of the invcrltion thRt any cornpound ormaterifll cflpuble of providing a soulce of Y~lnc iOllS in aqueous solution, which does not othcrwise intcrfere with ttle stntlility or oper~lhility of the resllltant ¦ aqueous ~inc plating sol~ltion, cnn t)e uti!i~ed.
l An electrolyte is providccl in t!le aqueolls pl~ting solution to provide i electricQlly chnrged ions capuble of conducting an electrical current. For example, an electrolyte may be selectcd froln any solllble c~lkali s11t of hydr~
chloric acid, su]fllric acid, sulfamate acid, ~iuobol~ic acid, or aceti~ acid, or from ammollium chloride, ammoniurn slllf~le, ammollium sulfamate, ammonium acetate, flll~monillm tluoborate or Inixtllle.s tllereof. It is fully within the purview of the invelltioll thnt other suit~ le elecllolytes Inay be utili~ed, provid~d they do not interferc eitl~er with the stability or operab;lity of ttle resultant aqueous zinc plating batll.
¦ Since the preferred embodimcnt of the novel ~inc platin~ solution of the invention is to be operable to ~rovide fl bright or lustrous xinc conting, at least I one brighterling ngent is added to the bflth. Tlle amount of such brightenillgi agent mQy be vflried to control thc clcgrec of brightne.;s required. ~or example, I
('OllVelltiOllal bri~haCnillg flgerltS SUC!h ~IS l~(!n~yli(lene acctone or c}chlol ob~n~al- I
dellycle mly l~e utilized. Of col~rse, if ~I senli-bligllt or dllll zinc (!oating is desired, n retlllcc(i nrllollllt of bri~ tctler mrly bc uîili~.ecl or lhe brightenil1g ~Igent 1 omitted frorn thc~ plnting bnth nll to~;ethel. Sllch nio(iificl~tion of thc specific i composition of lhe novel Yinc ~l~lting SOIlltiOll of lllc invention is fully within the skill of onc in the art.
2r~ ll Thc Y~inc pl~lting blltll of thc invcntion nl~;o cont~ s an orgflrlk ncid, or lt of nll ~ r'i~? ~ci(l. Pl~cl(~ y~ oi~ ol~ sodil~ b~llY,o~lt~ al~ d.
Ihe ~ uool~ inc plating sollltion ol` thc invclltion furthcr oontaills n novcl nnd improve(l ~rain~lea`ining ngent com~)risillg n polyllydric ~lloohol h~vin~ thre-or more hyllroxvl giOIlp6 sllbsLitllto~l willl ono or Inore oxynlkylerle g~rollps.

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~L~S~6S
The polyhydric alcohol is glycerin or sorbitol, having hydroxyl groups substituted wi-th either oxyethylene or oxyqropylene groups, or ~ombinations thereo~.

It is within -the purview of the invention that the number of oxyalkylene groups substituted on a polyhydric alcohol which can be used as improved grain-re~ining agent of the invention may be varied over the broad ranges mentioned above. The number depends upon the particular - polyh~dric alcohol which is substituted, the specific oxyalkylene group selected and variables of the zinc plating solution, such as pH, operating temperature and solubility. Accordingly, within the broad ranges men-tioned above, the number of oxyalkylene groups is not a limiting factor of the invention, provided the substituted polyhydric alcohol is soluble, and remains substantially soluble, in the zinc plating solutions o~ the invention.

When the grain-refining agent of the invention is glycerin substituted with oxyethylene groups, between 5 to : 30 moles of ethylene oxide are substituted for hydroxyl groups. Glycerin substituted with oxyp~opylene groups has between 3 and 15 moles of propylene oxide substituted for hydroxyl groups.

When the grain-refinning agent of the invention :is an oxyethvlene substituted sorbitol, between 6 and lO0 moles o ethylene oxide are substituted for hydroxyl groups. Sorbitol substituted with oxypropylene groups has between l and 20 moles of propylene oxide substituted for hydroxyl groups.

It is Eully within the purview oE -the invention that such polyhydric alaohols may have less than all available hydroxyl sit~s ~ubstltuted. However, i-t is preEerred that all available hydrox~l groups should be substituted with an oxyalkylene ~roup.

Furthermore, while oxyalkylene g.roups normally terminate with a hydroxyl group, the ter~inal hydrogen may be substi-- 6a - 1~56'~5 tuted with any radical qroup whicll does no-t interfere with, ~`~t~ or adversely ~ ~, thë solubility or performance of the grain-refining aqent in the zinc platiny solution.

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¦ It is nlso r~lly witl~in tllo ~llrVi(?W of tlle invclltiorl tt-lflt the substituted ¦ polyhydric ulcohol~; utilized ns grain-refining n~ents in accordQnce with the ¦¦ invention may cont~in one or more different oxyalkylene gro~ps. For example, Il glycerin having ~ome hydroxyl sites substitute~l with oxyethylene and othcr 1¦ hydroxyl siles subslilut~d witll oxypropylcno carl t~e utili~c(l in accordflnce with the invention. Fllrtllermore, grairl refining agents in flccordfiince with the present Il invention may contain blends of various different polyhydric alcohols substituted I Witll various clifferent oxyalkylcne gl`OllpS.
Il PreferAbly, nn anionic surfActflnt is also included in a zinc pl~ting solution lo ¦~ f the invelltion. I`or exnrnple, ~Ikyl slllrfltcs or slllfonat~s Ol alkyl aryl stllfonates I can be aclvuntflErously lltilixed. Most prcfcrrcd is thc so~iurn salt of 2-ethyl Il llexyl slllf~te.
Optiorlally it may also be desirable to incorporate a buffering agent, such ¦¦ as boric acid or salts thereof, in tlle novel zinc plating solution of the invention.
¦ Other conventional lypes of additivcs nnd Agents whicll ftre not incomp~tible i with tlle solubility or performance of the zinc pl~lling solutions of the invention, may be also incorporated, if desired. I;or exarnple, it is fully within the purview l of the invention thnt hydrotropes or like ndditives can be optionaUy included in I ~inc plating so]utions of the inventioll.

i In accordance with the preferrc~l embodimellt of the rnetho(] of the invention, an aq~leous, acid ~inc plnting sollltion of tl~e invention is used to! electroplale a brigllt and Illslrous Ainc coflting. I`he tcmpcratlJre of the zinc ¦ plnting solution is maillt~lilled betwean about 50F to ~20F (lnC to 4~G), and i prorerflhly hctweon ~i5 nnd ~I)or~ ~-3~~), witll n pll ran~irlg fr~m bctwecn 21; I nbout ~.6 to ~.G nll(l plefcrflL-ly belwcall ~I.D nrld r3,3, ~`~llrrant (~llSity rangill~
rrom nhol~t I to l~() nmp7 E-er s~ aro root (nmr-q/ft.2) cn~l bo n~)pli~d t~etwccrl fl lC anod~ n(l nn immorqe(l Inclr~llic wor!~r)ieco.
ln llO(!Ol'dU11(!~3 Witfl tl~e m~ od of tl~e inverltiorl l!tilizing the impl oved nqueous, acid Yinc plating solution, platinFs of 7~illC wl~ich ar~ bright ~lnd lustrolls . I

, ~lS~i9~S

over the entire r~nge of currcnt dellsity are obtP.ined. If semi-bright or dull zinc coatings are desired and le.~s hrightenin~ a~ent incorpor~ted in the ~inc plrlting solution n semi-bri~ht or chlll zinc co~ting will be produced ilnving exccllerlt n(31le.sion and n high rlegree of dllctility.
Wllile til~ thickness of the zinc contings obtuinec1 in accordance with the .
invention is not limiteci it l~s~ lly rflnges lrom L ctween 0.1 ~tnd n.6 mils ~0.0001 to o.noo6 inches) nndr prcfernL ly nl~ollt 0.25 Illils (0.0002 5 inciles).
In order to illustrute morc fully the in~proved f3qUaO1~9, ncid zinc plnting solutions and metl~od of the invcntioll tlle followin~ I.xalnp1es are set forth but nre not intended to limit the scope of the invention.
Lxllmple I
¦ An nqucous ucid zinc clllorido plating SO]UtiOIl ~Nas prepnled by admixture of the following: ¦
7~inc e~l~loride 34 g/l ll Potnssium chloricle 210 g/l j 13OI ic acid 26 g/l 1 2-ethyl hexyJ sulfate .
¦ svdium salt 21 g/l Ben~oic acid sodiurn salt 3.7 g/1 ~l t3en~yli(1el1e acetone 0.26 ~
i o-clllorobienæal(lel1yde 0.07 g/l C.lyccrin l?tlloxylntad 1.
witl~ 17 mol~s Or cthylcna oxidc 8.5 F/l Ihis 7~inc plating solutiol1 hl1(l n pll l etwoc!l~ 4.9 and 5.3 nl~(l n tempernture of 75P t~.9C). ~ steel panel was prcpnrcd in tl1e conventional manner llnd I E~lnCC(I h1 rl Stnndlll~CI IIUII Cal~ WO ilnlps of clectrical currciitlt was applied across the olcctrodes of thc coll for S mimltos so n.s to produce n cllrrel~t clensity rn-lgirl~ flolll nt~olll l to 1~0 nlllps/~l.2. Sollltioll Ilgitntion wrls provklcd ~!5 I by machullicu1 rnotion.
~\ilor r~ milllllc~ tlle i'low Of (.'lll'l`Cinl WIIS tc!l~ lulll~cl nnd punal ralnove(l for cxamil1alioll. I`llc p~.lnel wn-; co~:llcd willl a l~ri~ht nll(l lllstrous pl~ltill~ of . ~inc over th~ elltile rn~lge of clllrellt dellxitics.
l~e 2 ~0 E:xnmpl~ I wns rcpanted witll tllc cxccption that glycel in ethyoxylnted ~ S69 I
with 26 molcs of elhylene oxide ((!oinmel ( ially avail~ll>le un(ler the trade -~r~e MACOL ETG-26) was used ns the grnin-let`irlingr agent.
Ihe re~llltant pan~l exhibited a brigl)t nrld lustrous plating of æinc over Il the entire rull~c of cnrrcrlt densities. I
¦ Es~nmple 3 i Exnrnple I was repc~te~l, except tll~t glycerin ethoxylnted with S moles !~ of ethylen~? oxide w~s used ~s tl~e grain-refirling agent.
¦I The resultnnt panel exhibited a brigllt nnd ll~strolls plating over thc entire ¦l range of c~lrrent dcnsity.
' ¦~ amplc 4 ¦I Exnmple I was repented, cxcept thnt glyccrin cthoxylated with 30 moles f , of ethylelle oxidc wus used as ~lle gr~lin-rcfinillg ngent.
, The rcs~lltant p~nel ~xhihite(l a æinc plAting wi~icll WflS bright alid lustrous over tlle entire rnnge of curl ent density.
~ Exnmple 5 ¦l Example I was repeated, except thnt plating was conducted at an elevated li temperature which ranged between 120 and 1251~ ~18.~) to 51.7C).
The reslll tant zinc continbr on tl)e pnncl exhibi ted A bright and lustrous j, appearance over the entire rnll~,re of culrent dcnsity.
,, ExQmpl~ 6 T~or purpQses of comparison with the perforn~arlce Or a gr~irl-refinillg a~ent jl of ttlC prior urt, I xample S was r~pcated, exccpl thrlt a conventional grain-refining agcnt eomplising cetyl-stearyl alcollol etlloxylnted with 21i moles of ethylene !1 oxkle was uscd in place of the ~s~lb~;titl~tcd ~rlycerin rmatorial of the invention.
¦~ l`he æirlc plntill~ sollltion clou(lod nnd tilO grlrlirl-rerining ng~nt palti~lly s~pnlntc~l fram sOIlltiOIl fOrlnill~ lln oi]y filnl. I`hc rcs~lltatlt ~.inc platin~ on the pnllal oxhibito(l poor ~rnill rcfillolllont nn~7 al) oily sllllnce, nn(l wa~ cornmar-^ially ! llnaca~ptuble. ~ . I
Ex~mple 7 3U }~xarnple I wns rei)erlted, ~xcept that glyoerin having hydroxyl groups _9_ 6~365 Il silbstitlltc(i ~it!l 311 rrlolcs of ~?~ CllC o.;i(l~! IZIIll 1.5 IllOI~,'S of propyler~ xi(lc ¦! was utilized ns the grain-relininp; ngent of the invcntiorl.
¦l The resultant zinc coflting on the pnnel wrls hrip;ht flnd lustrous over the ¦ entire ran~e of current density.
S ¦; Exflmple 8 Xrlm~ e I wns repen ted, except thut glycerin having hydroxyl grollps ¦ substitutcd witll 12 moles of prop~ylene oxide (comrllercinlly flvailable under the trade rlr~i e Macol E IIG-12) was used rls the grain-refilling agent. ~ -ïhe resllltant zinc coating on tl~e pflncl was bri~hl rJn-i ]ustrolls over the entire range of current densities.
mple 9 I xflmplc 1 wrls rlgain repentecl, except that Sol l~itol etlloxylatcd with 50 oles of ctllylene oxi(!e w~s utilized as ti~e ~I'flill-l'Cfinillg ai.,ent.
I`he resultant ~inc coatin~ on the pallel W{IS hl i ;l~t and l~strous over the I entire range of current density.
~ltho~lgll the preceding speciîic examples nre presented solely for purposes 11 of illustlntiorl it is to be understood that SllCh ZirlC plllting~ SOIlltiOllS nn{] methods i~ of electroplating Yinc utilizing the snme in flccordallcc with the invention rnaybe !l altered, varied or modificd withollt departin~; from the spirit or scor)e of the 2a l, irlverltion ns defilled by th(~ r~l~r~cn(le(l claims.

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Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An aqueous, acid zinc plating solution substantially entirely free of any content of alkyl naphthyl ethers and alkyl naphthyl ketones for electrodeposition of zinc coatings and consisting essentially of:
(a) a source of zinc ions;
(b) an electrolyte which provides electrolytically charged ions capable of conducting an electric current;
(c) an organic acid or salt of an organic acid;
and (d) a grain refining agent comprising a polyhydric alcohol selected from the group consisting of glycerin having 5 to 30 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 3 to 15 moles of propylene oxide sub-stituted for hydroxyl groups, sorbitol having 6 to 100 moles of ethylene oxide substituted for hydroxyl groups, and sorbi-tol having 1 to 20 moles of propylene oxide substituted for hydroxyl groups.

2. The aqueous, acid zinc plating solution of Claim 1, further including at least one organic brightening agent.

3. The aqueous, acid zinc plating solution of Claim 1, where said source of zinc ions is a zinc salt selected from zinc chloride, zinc sulfate, zinc sulfamate, zinc acetate, zinc fluoborate and mixtures thereof and said electrolyte is selected from a soluble alkali salt of hydro-chloric acid, sulfuric acid, sulfamic acid, fluoboric acid, and acetic acid, and ammonium chloride, ammonium sulfate, ammonium sulfamate, ammonium acetate, ammonium fluoborate and mixtures thereof.

4. The aqueous, acid zinc plating solution of Claim 1, further including an anionic surfactant.

5. The aqueous, acid zinc plating solution of Claim 2, wherein said brightening agent is selected from benzylidene acetone and o-chlorobenzaldehyde.

6. The aqueous, acid zinc plating solution of Claim 1, further including one or more additives selected from buffering agents, selected from boric acid and salts thereof, and hydrotropes.

7. The aqueous, acid zinc plating solution of Claim 1, wherein said polyhydric alcohol has at least one mole of oxyalkylene substituted per available hydroxyl group, said oxyalkylene being selected from oxyethylene and oxypropylene.

8. The aqueous, acid zinc plating solution of Claim 7, wherein said polyhydric alcohol is selected from glycerin having 17 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 26 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 12 moles of propylene oxide substituted for hydroxyl groups, glycerin having 30 moles of ethylene oxide and 1.5 moles of propylene substituted for hydroxyl groups, and sorbitol having 50 moles of ethylene oxide substituted for hydroxyl groups.

9. An aqueous, acid zinc electroplating solution substantially entirely free of any content of alkyl naphthyl ethers and alkyl naphthyl ketones and comprising:
(a) zinc chloride;
(b) potassium chloride;
(c) boric acid;
(d) 2-ethyl hexyl sulfate, sodium salt;

(e) benzoic acid, sodium salt;
(f) benzylidene acetone;
(g) o-chlorobenzaldehyde; and (h) glycerin ethoxylated with 17 moles of ethy-lene oxide.

10. An improved method for electroplating bright and lustrous zinc comprising:
(a) providing an aqueous, acid zinc plating solution substantially entirely free of any content of alkyl naphthyl ethers and alkyl naphthyl ketones and consisting essentially of zinc ions, an electrolyte, an organic acid or salt thereof, and a grain-refining agent comprising a polyhydric alcohol selected from the group consisting of glycerin having 5 to 30 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 3 to 15 moles of propy-lene oxide substituted for hydroxyl groups, sorbitol having 6 to 100 moles of ethylene oxide substituted for hydroxyl groups, and sorbitol having 1 to 20 moles of propylene oxide substituted for hydroxyl groups;
(b) maintaining said plating solution at a tem-perature ranging between about 50°F to 120°F and pH of between about 4.5 to 6.5;
(c) immersing a metallic workpiece and a zinc anode in said plating solution; and (d) applying a voltage across said metallic work-piece and said anode to cause electroplating of zinc to occur on said metallic workpiece.

11. The method of Claim 10, further including in said plating solution at least one brightening agent.

12. The method of Claim 10, wherein said source of zinc ions is a zinc salt selected from zinc chloride, zinc sulfate, zinc sulfamate, zinc acetate, zinc fluoborate and mixtures thereof and said electrolyte is selected from a soluble alkali salt of hydrochloric acid, sulfuric acid, sulfamic acid, fluoboric acid, and acetic acid, and ammonium chloride, ammonium sulfate, ammonium sulfamate, ammonium acetate, ammonium fluoborate and mixtures thereof.

13. The method of Claim 10, further including in said plating solution an anionic surfactant.

14. The method of Claim 10, wherein said brigh-tening agent is selected from benzylidene acetone and o-chlorobenzaldehyde.

15. The method of Claim 10, wherein said zinc plating solution further includes one or more additives selected from buffering agents, selected from boric acid and salts thereof, and hydrotropes.

16. The method of Claim 10, wherein said poly-hydric alcohol has at least one mole of oxyalkylene substi-tuted per available hydroxyl group, said oxyalkylene being selected from oxyethylene and oxypropylene.

17. The method of Claim 10, wherein said poly-hydric alcohol is selected from glycerin having 17 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 26 moles of ethylene oxide substituted for hydroxyl groups, glycerin having 12 mole of propylene glycol sub-stituted for hydroxyl groups, glycerin having 30 moles of ethylene oxide and 1.5 moles of propylene oxide substituted for hydroxyl groups, and sorbitol having 50 moles of ethy-lene oxide substituted for hydroxyl groups.