CA2185554A1 - Processes for forming thin, durable coatings of ion-containing polymers on selected substrates - Google Patents

Abstract

Non-evaporative processes for coating ion-containing polymers onto selected substrates and the articles made thereby, which processes fundamentally comprise contacting a substrate with a dispersion or solution of an ion-containing polymer and especially a solventless dispersion of a perfluorosulfonic acid ionomer, and thereafter contacting the dispersion- or solution-wetted substrate with a solution of a salt or of a strongly ionizing acid of a sufficient concentration to cause an adherent coating of the ion-containing polymer to be formed on the substrate.

Description

W0 9sl24976 ~ P~
PROCESSES FOR FORMING THlN, DURABLE cobrlN6s OF ION-CONTAINING POLYMERS ON
SELECTED SUBSTRATES
Thepresentinventionrelatestoprocessesforformingthincoatingsofion-5 containing polymers on selected substrates, and to the articles made thereby. More particularly,butwithoutlimitation,thisinventionrelatestoprocffsesforformingcoatingsof such polymers on such substrates, using a surface active dispersion of an ion-containing ,ool~ ..h;~l,willwettheparticularsubstratetobecoated.
Examples of the known ion-containing polymers include the sulfonated 10 p~ y~ s~copolymersofethylenewithalpha-betaunsaturatedcarboxylicacidssuchas acrylicacidormethacrylicacidandp_.~;uv,v.a,Lo,,ionomers. The~_.rluu,v~c,,L~,,,ionomers include those with sulfur-based functional groups, phosphorus-based functional groups and carboxylicacidorcarboxylateru~,~L;-,"aliLy. Allofthesemateriâls~withtheexceptionofthe phosphorus-based perfl uorocarbon ionomers, are presently .~,.. ,..._ .. ' "~ _ " "~ .
The~c_.rlu~,,i".,Ledionomerswhichhaveasthefunctionalgroupssulfonicacid groupsorasaltthereofhavebeenofparticularinterest,andcommercialexamplesofsuch ionomershavebeenproducedintheacidformbyE.l.DuPontdeNemours&Co.,lnc.,under the Nafion~ trademark:
( CP2-CF2 )mt CF2-CP ) OCP2CF( CF3 )OCF2CF2S03}I
The Dow Chemical Company has produced ionomers having a shorter side-chain (acid-form) structure:
t CF2-CP2 )m( CF2--CF ) I

OCP2CP2S03~
30 The production of these ionomers is descri bed widel y i n the I iterature, for example i n United StatesPatentsNo.4,358,545and4,940,525,andiswellknowntothose'1 "' 1 ::',the p~ i. ' ionomerart.
Dispersions of copolymers of a non-acid, r~ ' ~., ' .' "~ unsaturated monomer with anl.:hy~ unsaturatedcarboxylicmonomerarewellknownintheart,andaredescribed5 for example in United States Patents 3,799,901 and 5,206,279, and in the references l therein. Ethylene-acryiic acid copolymers in particular are . ' "~ available fromTheDowChemicalCompanyunderthemarkPrimacor~,whichcontainfrom3to20 wei ght percent of the acryl ic acid monomer.

WO 95/24976 ~ r~ ~ 77 Dispersions of ethyiene acrylic acid copolymers are available from Morton dLiu..alunderthemarkAdcote-,butcanalsobepreparedbystirringahighacid polymer ~typical Iy 20 percent by weight of acryl ic acid monomer) with a sol ution of aqueous ammoniumhydroxideatfrom95to110degreesCelsiusforfrom30to90minutesinaclosed 5 vessel. Typically,0.8molesofammoniumhydroxideisusedpermoleofacrylicacidtomakeadispersion containing 25 percent by weight of ethylene acrylic acid copolymer. A surface active dispersioncanbepreparedtherefromforcoating~vlyt~t,arluv.v~ eOr ,uvl~ forexample,bydiluting4partsbyweightofthe25weightpercentaqueous dispersionwith96partsbyweightofanequal mixturebyweightofwaterandethanol.
A partial Iy su If onated pol ystyrene (or SPS) can be prepared for exampl e by the procedure outlined in United States Patent No. 3,072,618. An SPS polymer prepared in this fashion and containing 1.2 meq/g of dry polymer will dissolve in 1,4-dioxane. A surface adive solutionordispersionofthepartiallysulfonatedpolystyrenepolymercanthereafterbe prepared which by visual inspection provides a good coating on substrates like pvl~ arN~v~v~ JI .6"~01~ andpol~"." ,' ,e,bydilutinga2percentbyweight solution of the polymer in 1 ,4-dioxane with an equal volume of deionized water.Dispersions of the I rl uv, u,u I ru. .i. acid ionomers and of the perfl uorosulfonate ionomers have been made previously by processes as described for example in United 5tates PatentNo.4,731,263toMartinetal.(saltformplacedinsolutionordispersionat250deg.
20 Celsi us and elevated pressu res, then solvent removed at ' t i , ~re and resulti ng sol ids able to be redispersed at room i , aLu. _ in a variety of solvents), United States Patent No.
4,661,411 to Martin et al. (acid form of ionomer at 250 degrees Celsius, high pressures), United States Patents No. 4,433,082 and 4,453,991 to Grot and the references cited therei n (aci d or salt fonm), Moore and Martin, ~ I ,ùlogy and Chemical Properties of the Dow 25 Perfluorosulfonate lonomers~, ' ' u. . ,vlo;ules, vol. 22, pp. 3594-3599 (1989), and Moore and Martin,~Chemicaland'' ~.I-ùlo~ lPropertiesofSolution-CastP.rluu,u,ulrv,.
Ionomers~r~ u.., l~ ' vol.21,pp.1334-1339(1988). DispersionsoftheNafion~
ionomers are also available - . ' 'l~ in vârious equivalent weights which employ a lower ~ol:~ '' ,a~iv"astheliquidmediumorsolvent.
Thinfilmshavepreviouslybeenformedusingthese~_.rluv,v a,Lu,,ionomer dispersions by evaporative coating techniques on various substrates, as best seen for example in the.'..~ ,L;ùn~;lMartinandGrotpatents(suitablesubstratesbeingcatalystsupportssuch as alumina, silica, zeolites, carbon etc., u_. I . ' LUA.- Or glass-containing fabrics, ion exchangemembranesorporousdiaphragms,andwireorwiremeshelectrodes),inUnited 35 StatesPatentsNo.4,680,101toDarlingtonetal.and4,720,334toDuBoisetal.(onadiaphragm support),andinSzentirmayetal.,~SilaneCouplingAgentsforAttachingNafionto61assand Silica~ (on glass), Analyt. Chem., vol. 58, No. 3, pp. 661-662 (March 1986).

-2-Wo ss/24976 ;2il ~ ~ 5~
None of the coatings produced bythese earlier processes, however, have been entirely satisfactory. Especially in the case of substrates having an uneven or irregular surface to be coated, excessive amounts of the ionomer have been required to be employed to assure complete coverage of the substrate. The durability and strength of adhesion to the underlying 5 substrateofthesecoatingshavealsobeenlessthandesired.
Thepresentinventionconcernsnovelandimprovedprocessesforformingthin coatingsofion-containingpolymersandespeciallyofthe,,_.rl-,v.~,,ulF~ saltform ionomers on selected substrates, which comprise contacting the substrate with a colloidal, surface active dispersion of an ion-containing polymer and then contacting the dispersion-10 wetted substrate ~whi le still wetted with the col loidal dispersion or sol ution) with a sol ution of asaltorofastronglyionizingacidwhichisofasufficient.~ .,l,ali.,"tocauseanadherentcoating(whichmaybecontinuousbutisnotnecessarilyso)oftheion-containingpolymertobeformed on the surface of the substrate. This coating is typically on the order of less than 100 nanometers thick, and desirably is on the order of 5 to 10 nanometers thick.
An optiona I add itional step may i nvolve exchangi ng the cation of the ionomerafterthisinitialsaltoracidsolution-contactingstep,asbycontactingthe'~
substratewiththesameoradifferentsaltsolution,forexamplewithapotassiumsaltsolutjon ratherthanasodiumsaltsolution,wherethe..~ LA~l.a--y_~formoftheionomerisless effective than the original form i n coating the substrate i nitial Iy but is more amenable to a 20 particularenduseortofurtherprocessing,orpossessesaqualityorpropertymorefullythan the original salt or acid ~orm.
Afurtheroptionalstepmayincludetreatmentofthecoatedsubstrateatan elevatedtemperaturetoprovideimprovedcoatingadhesiontothesubstrateorforother purposes,aswillbedescribedbelow. Thoseskilledintheartwillunderstand"~a.e"" ' "~,25 thatthe'dispersions~inquestionhavecertain-l,a,a-~.i,Licsoftruesolutions,asnotedinU.S.
PatentNo.4,433,082toGrot; ~dispersions'is.u,,~_~.,_.,Ll~,nottobeconstruedaslimitingof these liquid ~o...y."ili.,.,,of ion-containing polymers.
Thus,thoseamphipatic,ion-containingpolymerswhichmaybeplacedinsurface active dispersions generally are of interest, and the ion-containing polymers with low ionic 30 ~ul~L;-~ (forexample,containinglessthan20molepercentoftheionizablemonomer)areparticularlyofinterestforformingessentiallycontinuouscoatingsonavarietyofsubstrates.
Ion-containingpolymerswhichwhenformedintoadispersionorsolutiondonotwetouta givensubstratetothisextent,thatis,whichdonotprovideacontactanglewiththedispersion-orsolL~Li.aA,~, Y 'substratea~ ,a~,.;.-~zero,arealsousefulbutaremuchlesspreferred.
Theacidsolutionswhichcanbeusedto~ul"e.~.,_.,Llycontactadispersion-or .vI.,Li~...._'' 'substrateaccordingtotheinventiveprocessesincludeaqueoussolutionsof thoseacidswhichare.-,....Liv.. "~knownorclassifiedintheartas'strong'acids,for example, nitric acid, I ,, ' ~ " ic acid or sulfuric acid.

Preferably, however, a salt solution will be employed. The optimum salt .o~ a~iu~inthesaltsolutionemployedinagiven~ Ldependsonthesaltbeing used,buttypicallyisinexcessofabout1 percentbyweightofthesaltsolutionandpreferablyis between about 5 percent by weight of the solution and saturation in the solution. Salts which 5 have been found suitable for use i n the present i nvention i ncl ude cations such as hydrogen, ~I kal i metals, al kal i ne earth metal s and transition metals, ammoni u m and ", ' ,; u. . .
cationsin. iulul,le.u,.,L;" ' .,withanyanionsuchassulfate,fluoride,chloride, bromide,iodide,carbonate,phosphate,acetate,hydroxide,nitrateu, li.;u.y^l. For perfluc,,u a,L,ùî,ionomercoatingsmoreparticulariy,sodiumchloride,sodiumcarbonate, 10 sodiumacetateandsodiumbisulfatehaveallbeenfoundespeciallyu#fulinforming essentially continuous coatings on substrates such as PTFE, although as suggested above, it may bedesirableafterformingthecoatinginitiallytoexchangeadifferentcationforthesodiumin the ;u" li ,. uuyl I contacting the sodiu" . ~A~I lal ,yC;I, perfluorosulfonate ionomer coating withasolutionofthecation. Particularexamplesof instanceswherein itwould be "Ldy_~,u,toperformthisadditionalstepwillbegivenhereafter.
As has also been suggested above, the durability and strength of adhesion of theionomer coating are enhanced in preferred a ' " .1 of the invention by annealing at an elevatedtemperature. Theoptimumannealingt~..,,u_.aLu,~tobeemployedinanygiven application will depend on the structure of the ionomer, the counter ion and the thermal 20 propertiesofthesubstrate- Ingeneral,however,thegreatesti..,~ inadhesiontoa polymericsubstrateisrealizedbyannealingthecoatingatatemperaturewhichisnearthe ionicglasstransitiont~ a~L~(T9)oftheionomerinquestionorneartheTgorcrystalline meltpointofthepolymericsubstrate,butbelowtheL~ ,i, a~ule~Ofthe ionomer and substrate.
Incertain~," ofthepresentinvention,forexample,wherethe p_. fu~ e or properties of the coated substrate are known to be or expected to be ll,;~k.,_,_ d~"_.,J~.,Ltosomeextent, itwill bedesirabletoemploymorethanonecoatingof ionomer. The processes of the present invention can be adapted to provide a plurallty of such coatingsonaselectedsubstratebycontactingthecoatedsubstratewithasecond,saltsolution 30 i nvolvi ng a d ifferent cation to increase the contad angle of the coated substrate pri or to dpplying an additional coating of lonomer (in the manner used in applylng the initial coating, namelycontactingwiththedispersionandthenwiththefirst,originalsaltsolution),andbyI, t,~dt;,,ythecoatedsubstratetûfurtherraisethecontactangle. Or,theheattreatmentstep alone may suffice to raise the contact angle of the substrate to an extent such that an 35 additionalcoatingmaybeapplied.Thisheattreatmentwillgenerallybeconductedata ~ lowerthanthat,~ ,~cilfortheannealing,dL~ l ,.i"gstep,and preferably fol lowi ng depositi on of the final coati ng the anneal i ng step wil I be performed.
~I

WO 95/24976 2 1 8 ~ P~ ~ 77 Theionomerswhichwillbepreferredforuseincoatingaparticularsubstratewill depend on the context of the coated article's application and use. For example, where chemical and thermal stability are necessary or desired properties, the 1,_. rlu~JI u~al Lv~ .
ionomersaregenerallytobepreferred,whereasinother ,," . andusesnotQquiring 5 the chemical and thermal stabi I ity of these materi a Is the sul fonated ~u!~ and ethylene-acrylicacidcopolymersaregenerallytobepreferred byvirtueoftheirlowercost.
Forthe particular ,, " ,s and uses .u,, , ' ' herein, however, it is considered that preferred ~ . .L " ,t, of the coating processes and coated articles of the present invention will be based on colloidal, surface active dispersions of a r._. ï l v,ul f~.. .;c 10 acid ionomer or ,.,_. i' v~ul r..., ionomer. Ionomers which are of the type sold by E.l.
DuPontdeNemours&Co.,lnc.undertheNafion~ markaresuitable,asaretheshorterside chain sulfur-based ionomers sold by The Dow Chemical Company and described by structural formu la above. The Dow Chemi cal Company's shorter side chain ionomers are presently more preferredwheremaximumioniccontentandsurfacewettabilityaredesired,andmore generallyarepreferredfortheir~ ', ' ' ~y L,anovel,solventless(organic)~_.rluu.~-Lon ionomercoating processwhich isdescribed more particularlybelow.
Dispensionsare~L.. _.- "~availableorhavebeenmadepreviouslyusing ,~,_.rluu,v,~ ...;cacidorperlA~uorosulfonateionomersofvariousequivalentweights,but ,U~-c~dbl~ lll-perfluorinatedionomersemployedhereinwillpossessequivalentweightsinthe 20 rangeofSûOto1500,andmostpreferablywillpossessequivalentweightsintherangeoffrom 550 to 1 200.
Any known method for making colloidal dispersions of ionomers having these equivalent wei ghts . ,: _: "y be employed, for example, dissolving sol id ionomer i n a mixtureofwaterandaloweralcohol(forexample,ethanolorpropanol)atelevated 25 temperatures and pressures in a closed vessel (such method being described in the ~.~,...._.ltio,~_dUnitedStatespatentNo A433,082toGrot)~ r. . '1~.
dispersions may also be used of Nafion~ ionomer in a lower al~ul r 1,~ solvent system at these equivalent weights Preferably, however, dispersions will be prepared from at least certain of these30 ionomersforcoatingaselectedsubstratewhich~ onlyasthesolvent. Usinga ,1~ . -L.._d dispersionispreferableinthatthe'' ' '-Ly,inhalationand ,_, l Lal concerns associated with an ~ ~I, ". solvent system, for example, are not present with water as the solvent for these dispersions.
TheshortersidechainionomersproducedbyTheDowChemicalCompanyare 35 especially preferred for use in the context of a solventless coating process, as has been mentioned previously, because they have proven amenable at equivalent weights of from 550 to1000,andespeciallyatequivalentweightsoffromSSOto800,tobeingdispersedinwater ~lloneinhighyields(wheretheyieldisdefinedastheamountofionomersolidswhichare _5_ Wo95/24976 1~.,~1~.s.~ 7 effectivelydispersedintotheliquidsolventdividedbythetotalamountofionomersolids attempted to be dispersed) and under moderate conditions.
Inthisregard,the'082patenttoGrotdoes. ,' thepossibilityofmaking dispersionsofupto10percentbyweightofperfluorosulfonicacidformionomersinwater 5 alone(theionomershavingequivalentweightsintherangeof1025to1500),ati, _ of at least 240 degrees Celsius in a closed vessel with stirring. rhe examples illustrating this process show pressures of upwards of 370 pounds per square inch (2.5 MPa), and yields in room t~ alu~edispersionsofabout27percent(after1oohoursagitationat24odegreesand37o psi)andof48percent(after18hoursat235degreesCelsius).
3ycontrast,room i , _dispersionscontainingfrom 1 to3weightpercent ofthe-' . ,livll-dlowerequivalentweight~acidformshortersidechainionomerscanbe prepared in the context of a solventless (organic) coating process of the present invention with stirringinaclosedvesselattemperaturesoffrom 170to200degreesCelsius,apressureoffrom 110poundspersquareinch,absolute(psia)(0.76MPa,absolute)to225psia(1.6MPa, 1~; absol ute), and over a ti me frame of from 1 to 3 hours with yields on the order of f rom 70 percent to 95 percent or greater bei ng . ' - L, _ ~a;l for an 800 eq u ivalent weight ionomer.
Preferablynpowderedionomerinthedesiredequivalentweightiscombinedwithwaterina closedvessel,andheatedtoat~ ,_.aLu._offrom180to185degreesCelsiuswithstirringfor about2hours,withthepressurebeingontheorderof145to165psia(1.0MPa,absoluteto1.1 20 MPa, absolute) The substrates which may be coated with ionomers according to the process of the present invention are numerous, and may desirably include for example fibers, powders, fabrics,articlesoritemsof, lyt~ -u_:l,,' ,a,pGI~ fluoride,fluorinated ~1:,,,~.,_ ",~, ,' .~copolymers(FEP),poly(vinylchloride),glass,pu!~,,,~, ,'~ carbon,steel, 25 platinum,,l,lu.uL.irluu,u_l;.,' ,_or~_.rlu~". " ,~..,'_:h~, t~:larluolu_:ll,!~ .e copolymers(suchasaresoldunderthedesignationTeflonPFA"byE.l.DuPontdeNemours&
Co., Inc.). Obviously, since the present invention is concerned with coatings, articles which comprise an outer layer or coating of any of the ~ ~ . d substrate materials may also suitablybecoatedwithanionomerdispersionaccordingtothepresentinvention. Instillmore 30 general terms, it is considered that the process of the present invention can be used to provide anionomericcoatingasatransitionsurfacebetweenanytwomaterialswhosesurfacesform(inthe absence of the ionomeric coating) a high surface energy interface.
One notable example of such an interface would be the interface between a rl.,c,u,uùly..,_. matrixmaterialandreinforcingfillermaterialssuchascarbon,ceramicsorglass 35 thatareoftenusedinPTFEtoreducecoldcreep,lowerthecoefficientofthermalexpansionand improve compressive strength over an unfilled PTFE in the context of PTFE bushings, bearings and low dielectric circuit boards, for example. The present ionomer coating process offersasimplealternativetocoronadischargeorcorrosivechemicaltreatmentswith,for W0 95/24976 2 1 ~ 7 example,sodiumamideorsodiumnaphthidethatareoftenusedtomakefluo,.",~
surfaces more wettable and thus more bondable.
Asforotherspecificuseful ,," - ofthepresentinvention,inthecontextof proton exchange membrane fuel cells, the catalytic sites must be accessible to the reacting 5 gasesandtoaprotonconductor. Athin(forexample,lessthanamicrometerinthickness) coatingofa~ uu,oc-"LunionomeronacatalystkuPportedoru-,,uju~,v-t~)wouldprovide aproton.~ ucLv~ vuLimpedinggasdiffusiontothe~ iVII interface. The , tluv,v~O-Lu--ionomercoatingenabledbythepresentinventioncouldalsobeusedinthe preparationofelectrolyticcapacitorssuchasthosedescribedinunitedstatespatentN
1û 5,136,474toSarangapnnietaltoprovidemaximumprotoncu..du~L,'~;Lyandmaximum interfacial area.
A particularly preferred application of the present invention, however, is for placing an ionomeric coating or plurality of such coatings, and especially a perfluorocarbon ionomercoatingorcoatings,onpc,lJt~t, '' ~ (PTFE)fibersandlorpowderstomake 15 the PTFE fibers and/or powders water--wettable. In this regard, PTFE possesses a number of desirable attributes, including excellent chemicalrtability. AsignificantbarrierhasexistedhowevertotheuseofPTFEincertain 0,~ "forexampleinthed_._lvju..._...ofl,ùl, ~ diaphragmsforchlor--alkali cells, due to the 1, ' ~"-1 vL;. nature of PTFE.
zO Variouseffortshavebeenmadetocompensateforortoovercomethe Jl,v~i~characterofPTFEinchlor-alkalidiaphragmsthroughthe;~,~u~,u~,OLi~"ofion-exchange materials. An example of these efforts may be found i n United States Patent No.
4,169,024toFang,whereinPTFE(orasimilarrluu,~ . )intheformofapowderorfibers, inanunsupportedporousornonporousfilm,inacoatingonaninertfabricorinaporous 25 reinforced structure (that is, a diaphragm) is chemically modified by reaction with a sulfur- or phosphorus-containing compound.
UnitedStatesPatentNo.4,720,334toDuBoisetal.isalso.., ;~..LaLi._,and describes diaphragms containing from 65 to 99 percent byweight of a fibrillated fluorocarbon polymersuchasPTFEandfrom1to35percenturn,.~,-u.O.L.a-~ionomer(preferablycontaining 30 carboxyl ic acid, sulfonic acid, al kal i metal carboxyl ate or al kali metal sulfonate functionality) basedonthecombinedweightoffibrillated rlu.,.., 1~..._. andionomer,andoptionally further containing wettable inorganic particulate material. The diaphragm is dried and secureduponanunderlyingcathodebybeingheatedtoa; , _ _belowthesintering .~.,.,.,_._ _ofPTFEforatime. Theionomercanbeil,c~.~ . 'inthediaphragmby 35 cod~,~v~iliv~fromaslurrywiththeionomerbeingincludedasasolid~gelorsolution~bybeing coated on either or both of the flu.,. v.O, I,v,~ fibrils and inorganic particulate and then depositedfromaslurry,orbybeingextrudedinadmixturewithther;uv,vpol~ beforeitis fibrillated. Specific coating processes for coating the PTFE fibrils are described, including Wo 95/24976 r~ ... 5/Q~77 mi xi ng PrFE powder with a sol ution of ionomer i n a ~ solvent under high shear conditions, then dispersing the coated fibrils by blending with water and some surfactant.
Tl ,_, . 't~ materials are deposited onto the cathode from the resulting slurry.According to one ' ", ._. ,l of a coating process of the present invention, in 5 contrast, PTFE powders or fibers are initially mixed with a colloidal dispersion of a p~.nuu~v~ulru~ ionomerwhichprehrablyisproducedfromtheshortsidechain,acidform ionomer produced by The Dow Chemical Company and described above, and which has an ~quivalent weight of from ~5û to 1200.
This colloidal dispersion can be made, for example, by acid washing a film of the 10 acid--form ionomer, rinsing to neutrality with deioni~ed water, and then converting the film to the sodiumformoftheionomerbysoakinginsodiumhydroxide. Thefilmisthenrinsedto neutralityandoven-dried,afterwhichadesiredweightofthefilmisplacedinaglasslinerand mixed with a sufficient quantity of a suitable solvent, for example, 8 mixture of ethanol and water, to gi ve a sol uti on or dispersion havi ng an ionomer .u, ..~. ,t, _ ~ of preferably f rom 5.0 percentbyweightto7.0percentbyweight.
After sealing the liner in a stainless steel reactor, and purging with nitrogen, the reactor is stirred and heated to a h~ alul e at least on the order of 160 degrees to 180 degreesCelsiusforfrom1to3hours,producingapressureina11iterreactorof 180to220psig 20 (1-2 MPa, gauge to 1.5 MPa, gauge)- The reactor is then allowed to cool, the excess pressure bled off and the contents filtered through a 60 to 80 micron fritted glass filter. The resulting .-",.~.,l-ale.ldispersionisthendilutedwiththe~ oll. mixturetofinallyprovidethe desiredandpreferreddispersioncontaining 1 percentbyweightofthe,c_.rluc,u,~lru., ionomer.
Alternatively (and preferably), perfluorosulfonyl polymers in powder form can beusedinsteadofthe~.Fu,~,.,_.-liu.._~iu~ '' ,andthepowdershydroly~edinsodium hydroxide and dissolved and processed as described above. Other known methods of making a dispersion of the ,.,_. . ' u~ul F~,. . ionomer can be used without limitation as well.
ContactincJ a powdered PTFE substrate with the ~ 'c hc,lh based dispersion 30 madebythisprocesspreferablyinvolvesmixingthedispersionandPTFEpowderinaO.015to1 ratiobyweightofionomersolidstoPTFE,onadrybasis. Thisratiocanbeadjusted c,~ - uu~ to achieve a doughy, handleable mass. Where PTFE fibers, coupons or fabrics, etc.,areinvolved,ofcourse,thesesubstratesmaybesprayedwithordippedintotheionomer dispersion and the excess allowed to drain before contacting with a saltsolution.

3!i Theliquidcoatedsubstrateisthenstirreddirectlyandwithoutdryingintothesalt solution(inthecaseofcoatedPTFEpowdersorfibers)orimmersed(forcouponsorthelike) directly in the salt solution.

W0 9s/24976 2 ~
Suitablesaltsolutionsare(forthecoatingofPTFEmaterialstomakethemwater-wettablewiththe ' ~.ul;. -baseddispersionsortheionomerdispersionsinwateralone) formed from water and from the water-soluble salts of the alkali, alkaline earth or transition metals, strong acids, and the ammonium salts of ammonia, the primary, secondary, tertiary or 5 quaternary amines. Preferred salt solutions are prepared from the ~ 'ul~ sodium and magnesium salts for forming an initial coating on PTFE, and of these ~as has been previously indicated) sodium chloride, sodium acetate, sodium carbonate and sodium bisulfate are particularly preferred For purposes of achievi ng maxi mum . . . ~ or for addi ng subsequent coatings, it will be preferred to then contactthe coated PTFE with a potassium or 10 ~incsaltsolution,andforaddingsubsequentcoatingstoalsoheattreatatanelevated temperature,forexample,upto300degreesCelsiusfor20to30minutes. Thenthesingle-coated substrate is contacted with the dispersion, exposed to the sodium or magnesium salt solution,rinsed,exposedtothepotassiumor~incsaltsolution,rinsed,heattreatedandsoon untilthelastcoatingisappliedthatisdesired,withthefinalheattreatmentbeingan annealing of the coated substrate.
The quality of an ionomer coating produced according to the present invention, as assessed by contact angle measurements on the coated PTFE substrate, is ultimately affected bytheionomer.v..~ aLiu,,inthecolloidaldispersion,bythedispersion'ssolvent .u...~,u,ilio-.,andbythetemperature,salt~un-~:,-L,aLiu,,andpHofthesaltsolution. Eachof 20 thesevariablesinteractwitheachotherandwiththesalttypeandtheionomerstructure. Itis expectedhoweverthatthoseskilledintheartwillbeabletodeterminetheoptimum .u. .,Li"..~ion of these variables for a given application (including the coating of substrates otherthanPTFEand/orforpurposesotherthanimpartingwater . ' ' "'~.~ Ll.~ v)by following the approach of the illustrative Examplff provided below.
For placi ng a coati ng of an 800 equi valent weight perf luorosulfonate ionomer(derivedfromTheDowChemicalCompany'sshortsidechain~ a.L~".ionomer)on PTFE for making the PTFE essentially ~c _. . ._. ,tl~ ' ' ' ' from an ~' ' "
based dispersion of the ionomer prepared as described above, it would appear at presentthat fromO.25to2.0percentbyweightoftheionomershouldbedispersedinanaqueousethanol solutioncontainingfrom25to100volumepercentofethanol,andthatthesaltsolutionshouldideallybefrom 16to25percentbyweightofsodiumchlorideinwater.
For PTFE samples which are to be annealed, most preferably this ionomer dispersion should contain 1.6 percent by weight of ionomer in a mixture of 63 percent by vo~umeofethanolinwater,andthesaltsolutionshouldbea25percentbyweightsolutionof 35 sodi um chloride in water at a ' , ~ of 65 degrees Celsius.
For PTFE samples which are not to be annealed, the br~st results are seen with an ionomer d ispersion contai ning 1.8 percent of the ~_. . ' u,ul, ionomer in a 60 g wo 95n4976 ~ P~
percentl40percentmixtureofethanolandwater,andasaltsolutionof25weightpercent solution of sodium chloride in water at a temperature of 55 degrees Celsius.
Asolventless(thatis,employingonlywaterastheliquidmediumofthe dispersion) coating process of the present invention is preferred, and can be carried out in 5 several ways depending on the ionomer type employed and the nature of the dispersion to be used. Forexample,fortheshortersidechainionomersproducedbyTheDowChemical Company, an integrated coating procffs would initially and preferably involve the preparation of adispersioninwateroffrom1to3percentbyweightofa~._.rl,.~ "ulF~,,.;.acidform ionomerhavinganequivalentweightoffromSSOto1000,andespeciallyfromSSOto800 10 inclusive,bytheproceduredescribedabove. Alternatively,anavailableal~.,l,.a:/~ based dispersion could be .v" . . ~io~ processed to remove the alcohol . Where the ionomer is a perfluorosulfonic acid ionomer of the Nafion~ type, initially a dispersion could be prepared in waterofupto10percentofanionomerofanequivalentweightoffromS50to1500, accordingtotheprocessandundertheconditionsspecifiedinU.S.Pat.No.4,433,082toGrot, ormorecommonlya~ . "y_. ' '' L'~ h~lh baseddispersionwillagainbe u," . _. ~ Li~ procffsed to remove the alcohol, The resulting dispersion is then added to a PTFE powder, for example, which willpreferably have been subjected to intensive shearing in waterto produce uniformly-sized PTFE
particles,ortopreferablypreshearedPTFEfibers,ortoamixtureofPTFEin, )~ .' 'g all ' 20 form and in the form of fibers. The mixture is then subjected to hi~h shear conditions generally .~,.,~,"o"d;..~toabladetipspeedonthemixerusedof800ft./minute(240..._t~.,/ `or greater,foratimesufficienttocoatthePTFEsubstratewiththeionomerandachieveauniformsl urry, with care being taken to not create such heat by excessive ~ leal i l l~ as might causethecoatedPTFEtobegintoclumptogether. Itisimportanttonotespecificallyherethat 25 theliquidsinquestionaretobeaddedtothePTFE,asopposedtothePTFEbeingaddedtothe water or dispersion.
The resulting ionomerto PTFE solids ratio will generally be O.û05 to 1 by weight or greater,preferablybeingfromO.005to1toO.015to1andmostpreferablybeing ay,~ 0.015to1,withsuffficientionomerandPTFEbeingpresentforagivenvolumeof 30 waterto achieve adequate shearing of the solids and coating of the PTFE bythe ionomer. This minimumsolidslevelcanreasonablybeexpectedtovarywithdifferenttipspeedsanddifferent mixing conditions and with different equipment, but can be determined through routine . .
Thoseskilled inthediaphragmartwillappreciateatthispoint,thatbecausethere 35 isnoneedforarinsesteptoremovetheloweralcoholsolventfromthecoatedPTFEmaterjal,theionomercoatedPTFE , Ll,~.~ 't~. becontactedinsituwiththerequisitesaltsolution,in thedrawvatfordrawinga~ diaphragm. Alternatively,forother,, " ,sand usesthecoatedPTFEmayberemovedfromasaltsolution,rinsedwithwatertoremoveexcess W095124976 ?1~5~4 r~ s~, sa It and air-dried. Most preferably, however, the coated PTFE for such other , " ~ and uses is kept wetted afterthe optional rinse step, in that coated PTFE which has been dried generally requires vigorous agitation or stirring to be rewetted.
Both of the above-described coating processes (that is, involving coating from a5 dispersion of ionomer in an organic solvent (commonly a lower alcohol) and water, and from an ionomeric dispersion prepared in water only or from which the organic solvent has been removed)produceanevenlythinionomericcoatingwhichissufficientlydurabletoberinsedin t being substantielly removed, but which can be removed with mechanical abrasion.
Asindicatedpreviously,thedurabilityandstrengthofadhesionoftheionomer coatingcanbeenhanced(tothepointwherethecoatingmaynotberemovedwithhand rubbing)wheredesiredforagivenuseorapplication,byannealingthecoatedsubstrateatan elevated temperature below the v~ on temperature of the ionomer coating. The optimumannealing;, .,~u,einagivenapplicationis,again,generallydependentonboth the structure and salt form of the ionomer and on the nature of the substrate. Adhesion of the coatingtothesubstrateisgenerallyimproved byannealing nearorabovetheglasstransition temperature of the ionomer. More preferably, for achieving the greatest adhesion and durabilitywiththeionomercoatingofapolymericsubstrate,theannealingwilloccurnearthe glasstransition , ~(T9)ofanamorphouspolymericsubstrateornearthecrystalline 20 melting point of a crystalline polymeric substrate. Thus, for PTFE coated with an 800 equivalent weight, shorter side chain perfl uv. ~-,u I r. ionomer of the type made by The Dow Chemical Company(havinganionicT90f250degreesCelsius),thegreatestdegreeofadhesionand durabilityisgenerallyachievedwithanannealingofthecoatedPTFEatai~, _offrom 330 to 350 degrees Celsius for from one to 360 minutes, while for ~vl~ . :. ., " '~ fluoride 25 substrates coated with the same ionomer, the preferred anneali ng conditions correspond to a temperature offrom 160to 170degreesCelsius maintained forfrom one to 360 minutes.
It should be noted, however, that the benefits of enhanced adhesion may be offsettoanextentinthatwiththere-orientingofthesubstratesurfaceundertheseconditions, somemigrationoftheionomerintothesubstratecanbeexpectedwithanattendantlossof 30 some wettability, for example, in the sintering of a chlor-alkali diaphragm including ionomer-coatedPTFE. Cv~ tly,theadhesionanddl ~ ll,alcanbeachievedunderselected annealingconditionsforagivenenduseorapplicationshouldbeweighedagainsttheeffect of adecreaseinwettabilityorsomeother~,,vy_.Ly~ l,mayresult,todeterminewhetheritis desirable to achieve such enhanced adhesion and d~ tv, ~I ,è end use or application.
In the context of chlor-alkali d iaphragms employi ng the above-described, preferredcoatedPTFEpowderand/orfibersinsomefashion,ithasthusbeenfoundthatthese coatingsinalkali metal perfluorosulfonatesaltform arestableand remainwettableafter exposuretothe335to350degreeCelsiusi ,. ~;atwhichthediaphragmsare Wogs/24976 ?~8~ , .v"._.,Li~ sinteredandbonded,andthatthecoatingsareessentiallyp_., ._.,~ly ~dheredtotheunderlyingPTFEsubstrate(tothepointthatordinarycellophaneadhesivetapeapplied to a coated and annealed PTFE coupon will not visibly remove the ionomer coating).
Those skilled in the art will appreciate from the foregoing that for substrates 5 otherthan PTFE and for,, ~sotherthan making PTFE ~ -. different ionomers may be useful or desirable (having different backbone structures, different tu.,~ .n..lili_.orbeingindifferentsaltforms),ionomersofdifferentequivalentweightsmay be usef ul or preferabl e, salt sol utions for example of different .~ .. ." i , _.
and/or pH's may be useful or preferred, and anneal i ng may not be appropriate or may 10 a~JIv~ involvedit~,,"~t~,,"_ a~,A,~, Because of the variety of substrates and ionomers which are, , l;
herein, and because of the variety of ~,, ,, and contexts i n which the present ionomeric coatingsarepotentiallyusefulastransitionsurfaces,itisnotpossibleorusefultofullydescribe herein al I of the possi ble ~o, ~.bi " ,, of su bstrates, ionomers, a nd applicati ons whi ch are of interest. Itisconsidered,however,thatthese.v,.,Li--a~i~,-,,canbepracticedwithoutthe exercise of further inventive skill, given the teachings above and given the examples provided hereaher:
Illustrative ExamDles Examoles 1-4 An ionomer of the type produced by The Dow Chemical ~ y ~ prepared by.~ . i a~iOn of CF2=CF2withCF2=CFOCF25O2Finanemulsion, :~ iLa~NII I system.
The resulting polymer was isolated, dried, pressed into a film and hydrolyzed with 25 wt.
percent NaOH to give a perfluorinated sodium sulfonate form ionomer. Aher being water-washed to neutrality, the film which contained 1.25 , . of sulfonic groups per 25 gram of dry weigm was cut i nto small pieces and 5 parts by weight (on a dry basis) of these fi I m pieceswereplacedinastirredpressurevesselwith95partsbyweightofamixtureofequal partsbyvolumeofethanolandwater. Thevesselwasthenheatedwithstirringto165degrees Celsius for 4 hours. Aher cooling, the percent solids of the resulting dispersion was determined to be 5.1 wt. percent by r Jr, a ~ y a weighed sam ple to dryness and weighi ng the residue.
30 The colloidal dispersion was colorless with a sl ight haze.
ThisdispersionwasusedtocoatTeflon~7CPTFEpowder,astripofPTFEfilm,a pol~,..., ,' )~couponandasteel coupon. Forthepowder, 100gramsofthe, placed i n a bea ker and 700 grams of the dispersion added thereto. The m ixtu re was agitated with a Lightning D51010~ stirrer at 600 rpm for about 20 minutes until a uniform slurry was 35 obtained. This slurry was vacuum filtered using a medium to coarse filter paper, and the wet cake placed in a solution of 5 weight percent of sodium carbonate in water at room _andallowedtostandfor15minutes. Thetreatedpowderwasthenredispersed with the stirrer, and recovered by vacuum filtration. The filter cake was washed to neutrality Wo95124976 21 8~ r~l,u~ , bythreeiterationsofdispersingthewetcakeindeionizedwaterwithagitationinahighshearblender and recovering by vacuum filtration. The powder remained easily wettablethroughoutandwouldsinktothebottomoftheLl~.,d~ ..agitationwasstopped,andwas observedtorewetafterdryingbystirringwithdeionizedwater.
Forcomparison,asampleofthe, ' ~ treatedwiththeionomerdispersion, filtered and placed in a ~1~. ,d~. ' deionized water. After blending for 2 minutes, the ' ~ observedtoloseitswettabilityandcoatthewallsoftheblenderandtofloaton the surface of the water.
ForcoatingthePTFEfilm,a 1/2inch(1.3cm.)widebythreeinches(7.5cm.)10ng 10 stripofPTFEfilmwascleanedwithacetoneanddeionizedwater,immersedformostofits lengthintheionomerdispersionforabout10seconds,removedandallowedtodrainbriefly, then immersed in a 5 weight percent solution of sodium carbonate in water at room t~..",~ t~,,eforabout10sêconds. Thefilmwasthenwashedwithflowingdeionizedwaterto remove any loose material and excess salt, and treated with an aqueous solution of Safranine O~ cationic dye dispensed with an eye dropper. The ;on~ ' area remained wetted throughout all of these steps and absorbed the dye, to leave a uniform reddish pink coloration which was not removed by rinsing with deionized water butwhich could be removed with adhesivetapeorbyrubbing AcoatedPTFEfilmthatwasnotimmersedinthesodium carbonate solution dewetted and would not hold the dye.
The pol~ e coupon when coated with the dispersion and immersed in a 26 wt. percent solution of sodium chloride and water at room i , ~ provided a wettable, uniformlydyedsurfacebythesameprocedures,asdidthedegreasedsteelcouponwhichwas coatedandimmersedinthesame26wt.percentsodiumchloridesolution.
Example 5 A PTFE film was coated with the ionomer dispersion of Examples 1 4, immersed in a5weightpercentsolutionofsodiumcarbonateinwateratroomtemperatureandthefilm rinsedtoremoveloosematerialsandexcesssalt,butthefilmwasnottreatedwiththedye.
Thefilmwasthenannealedbyheatingslowlyfromroomtemperatureto350 degrees Celsi us (for example, at about 2û degrees per mi nute) i n a 1: '1 r~.,kal ~ 5880 gas 30 ~1..3.~ ., h oven,andbeingheldatthist~..."_. a~U.~. for 1/2hourbeforecoolingtoroom temperature(typicallyoveraspanoffrom 10minutesupto2hours).
After being cooled to room temperature, the film was treated with the Safranine O" dye solution. The coated part of the film absorbed the dye and acquired a reddish-pink colorationwhichwasnotremoved byadhesivetapeorbyrubbing.
The heat treated or annealed fi I m (and more specifically the coated portion thereof)wasobservedtohaveacontactanglewithwaterofabout10ûdegreesaftercoolingin air,of about88degreesaftersoakingindeionizedwaterfor2hoursandofabout79degrees afterbeingimmersedindeionizedwaterfor20hoursat70degreesCelsius. Anuncoatedfilm Wo gs/24976 ~ r~ 7 that had gone through the same heat cycle was observed to have a contact angle with water of about 126 degrees on cooling, and this contact angle was essentially unchanged aher soaking inwaterfor2hours. Itwill.u, , 'ybepreferredinthecontextofcoatingandannealing ~ PTFE substrate to provide . . ' "' Ly thereto, as for example in the u ~a.~u, . of a 5 chlor-alkalidiaphragm,toemployawatersoakortorewettheannealed,coatedPTFEby stirring in water before placing the diaphragm cell in operation.
The method used for maki ng these contact angle . , .., a nd those made insubsequentexamplesbelow,involved, "' ..Lio~oftheparticularannealed,coatedPTFE
couponinwateratambientl, alu..~,generallyoveraperiodof16hoursorso.
1û Unannealedsampleswererinsedaftercoatingandlehimmersedinwateruntilthecontact ~ngle was ~.t~. " ' A given coated and salt solution-immersed PTFE coupon (annealed or ~,., )~, ' 1`wasthereaherremovedfromitsdeionizedwatersoakandpatteddry,then placed on the stage of a Kernco Contact Angle Meter, Model G-1 contact angle measuring 15 deVice;several~ .,t~(10to14 ...,~ )weretakenofthecontactanglewith water of the coated coupon on this device. Where the coupon in question would not lie flat on thedevice,114inch(0.6cm.)diameterdiskswerecuttherefromusingaholepunchandthe contact angles determined on the sides of the disks which had not been exposed to the punch.
Twomeasurementsweremadeusingtheoppositeedgesofeachdisk,andthe ~ .L.
20 averaged as with the coupons.
ExamDles 6-2û
Adesignedexperimentwascarriedouttodeterminetheeffectofvarious conditionsincoatingtheionomerdispersionofthepreviousexamplesonPTFE,withrespecttothe contact angle of the coated PTFE with water. The variables explored were ionomer 25 .~,,,....~raLùninthedispersion(intherangeoffrom1toSpercentbyweightinamixtureof equal parts by volume of ethanol and water), the ~O~I~el ,t,aLion of sodium chloride in the aqueoussaltsolution(from1to25percentinwater),andtheeffectofperformingmorethan one ionomer coating cycle without performing a heat treatment in between these coatings.
Allofthesolutionswereatroom~ .aL,~,-(a,~.,u-~ '~25degreesCelsius).
In terms of the general proced ures fol I owed i n this designed eA~._ . i t, the PTFEcouponstobecoatedwereinitiallywashedinacetone,rinsedwithdeionizedwaterand dried. Thereaherthecouponswereimmersedintheionomersolution,removedfromthe ionomersolutionandallowedtodrainforfromSto10seconds,thenimmersedinthesalt solution. Thecouponswerethenremovedandrinsedindeionizedwater. If asecondcoating 35 wastobeapplied,thesestepswererepeatedwithoutdrying. Thecouponswerethenairdried andannealedbyheatingtobetween335and345degreesCelsiusandholdingatthis temperature for 30 minutes. Aher cooling, the coupons were soaked in deionized water overnight. Thecouponswereremovedfromthedeionizedwater,patteddryandthecontact Wo gs/24976 2 1 ~ 5 ~ ~ ~ r~
~n~le with water determined in the manner described above. The conditions and results from thesevariouscouponsareshownbelowinTable1,alongwith",~ "._"t.conductedon uncoated,annealedanduncoated,unannealedPTFEcouponsforcomparison. Basedona statistical analysis of the data therei n, the opti m um ~ is pred icted to be !; obtainedwithadispersioncontaining 1 percentbyweightofionomerandasaltsolutionof25 weightpercentofsodiumchlorideinwater. Asecondionomercoatingwasnotobservedto haveabeneficialeffectintheregionoftheminimumcontactangle,absentaheattreatment between coatings.

3û
3~

5~
W095/24976 ? 1~ 77 Table 1 lonomer Salt CO~I~e,,~la~iOll C~n~ t~a~ ContactAngle . .
Sample (Wt. Pd.) (Wt. Pct.) (Av4., Deqree5) Std. Devlatlon Uncoated, NA NA 111.2 2.10 Unannealed PTFE
Uncoated, NA NA 102.3 2.56 Unannealed PTFE
Uncoated, NA NA 128.8 3.19 annealed PTFE
Uncoated, NA NA 134.9 1.64 annealed PTFE
Uncoated, NA NA 128.8 2.76 annealed PTFE
2 Coats, 1.0 25.0 92.5 7.05 Annealed 1 Coat 1.0 13.0 105.1 16.28 2 Coats 1.0 1.0 123.9 6.53 3Coats 1.0 13.0 118.0 10.67 1 Coat 3.0 25.0 108.5 12.98 3 Coats 3.0 1.0 124.7 4.57 2 Coats 3.0 13.0 117.3 10.89 2 Coats 3.0 13.0 105.3 10.49 3Coats 3.0 25.0 116.6 7.18 2COâtS 3.0 13.0 114.1 8.57 1 Coat 3.0 1.0 129.4 4.74 2Coats 5.0 1.0 117.3 13.05 1 Coat 5.0 13.0 103.2 27.20 2CoatS 5-0 25.0 109.9 16.22 3 Coats 5.0 13.0 ga4 8.39 ExamPles 21-35 Aseconddesignedexperimentwascarriedouttodeterminetheeffectsofthe 35 i, dtu~ ofthesaltsolution,ofthealcohol(ethanol)~o.,~-:, It-dtil.lli intheionomer dispersionandoftheionomer~on~e,lt,aLoninthedispersiononthemeasuredcontactangle of PTFE coupons coated and annealed as in previous examples. A single coating was applied in Wossl24976 ~ 85~ P~./~ 7 al l instances~ and the salt ~o~ a Liol ~ held constant at 25 percent by weight of sodi um chloride in water.
The ,.... ,I .:, A -JI .~ associated with these coupons and the results of contact angle testing thereon are shown in Table 2 below:
Table 2 Salt lonomer Ethanol in Solution COI.. lLlali~,ll Dispersion(Vol. Temp.(Dec. ContactAngle Std.
NVt. Pct.) Pct.) Q (AY9. Dea.) Deviation 1.75 5û.û 25.û 107.30 6.78 1.00 75.0 25.0 98.00 5.68 1.ûû25.0 25.0 112.2C 1Z.42 0.25 50.0 25.0 1 18.14 5.60 1.75 25.0 45.0 103.10 9.79 1.00 50.0 45.0 108.00 8.30 0.25 75.0 45.0 128.28 4.25 1.75 75.0 45.0 95.71 6.78 0.25 25.0 45.0 116.00 10.40 1.00 50.0 45.0 82.50 9.73 1.00 50.0 45.0 98.50 8.31 1.00 75.0 65.0 92.50 8.75 1.75 50.0 65.0 87.21 5.47 1.00 25.0 65.0 95.57 20.87 0.25 50.0 65.0 121.80 5.50 The data in Table 2 show that the contact angle is lowered, and wettability improved, by heating the salt solution in the exemplified process to a i , ~ of 65 30 degreesCelsius,andfurthersuggestthatatthis~ .a~u._theoptimumionomer ~v,)....t,alionshouldbenear1.5percentbyweightofthedispersion,withtheoptimum alcohol~v~ llali~ inthedispersionbeing63percentbyvolumeofethanolinwater~
Together, the foregoing examples showthat the coating quality as measured by contactangleisoptimum(undertheconditionstested)fordispersionscontainingfromO.5to35 2.0 weight percent of the ionomer in 40 to 75 percent by volu me of ethanol in water, and is improved byhighsodiumchloride~vl~ alio~sand l,;gl,~ res(thatis,above 65 degrees Celsius) in the salt solutions employed.

W095/24976 7 1 ~
Exsmples 36-50 The designed experiment of Examples Z1-35 was repeated on unannealed coated PTFEsamples,withtheresultsshowninTable3. Thecontactanglesfortheunannealedcoated PTFEsamplesareshowntobesubstantiallylowerthanforthe.u,,~,~,.-,,ui.,~annealed,coated 5 PTFE sam ples, but the effects and trends observed i n Examples 21-35 are also observed i n Table 3.
Table 3 Sr~lt lonomer Ethanol in Solution C".~ t.. Li~,., Dispersion(Vol. Temp.(Dea. ContactAngle Std.
1~t.Pct.l Pct.) C) (Ava Deq.) Deviation 1.75 Sû.0 25.0 93.û8 6.ûS
1.ûO 75.0 25.0 83.50 6.2û
1.00 25.0 25.0 99.00 6.87 150.25 S0.0 25.0 100.00 4.84 1.75 25.0 45.0 79.33 5.51 1.00 S0.0 45.0 79.91 8,11 0.25 75.0 45.0 105.16 4.68 1.75 75.0 45.0 76.75 6.71 200.25 25.0 45.0 90.16 6.27 1.00 S0.0 45.0 77.16 4.85 1.00 S0.0 45.0 89.00 10.88 1.00 75.0 65.0 91.58 8.26 251.75 50.0 65.0 69.91 10.49 1.00 25.0 65.0 97.08 12.00 0.25 S0.0 65.0 89.41 6.03 wo gs/24976 2 ~ 8 5 ~
Examples 51-56 P~'~t~t.~ v~;I.,'~.,ecouponswerecoatedintheseexampleswithdispersions oftheionomerutilizedintheprecedingexamples,atseveraldifferent.u.~c~.,t,aliùf~s~ The coatedcouponswerethenexposedtoabasic5weightpercentsolutionofsodiumcarbonate 5 (Na2CO3)inwateratambienttemperature(25deg.q. Thecouponswereallthenannealedas described previously. The contact angles were then determined for specimens that had and that had not been ~ , ' ' ' (soaked) prior to . . .__,.,. . ,t of the contact angle by immersion in deionized water. The results from these tests are shown in Table 4: Table 4 1 0lonomer Cvll.ell~lalivf~(Wt. ContactAngle Std Pct.) ' . "' '? (Avq., Deqrees) Deviation 1.00 Yes 78.5 3.69 1.00 No 123.5 3.42 15 2.50 Yes 79.3 4.78 2.50 No 103.8 2.50

4.60 Yes 78.5 3fi9 4.60 No 102.5 3.66 Thesedataagainsuggestthattheannealed,coatedPTFEmaterialsgenerallyare improvedinwettabilityafteraninitialperiodof ~ '' ,inwater,andthat,incommon with the earlier sodium chloride ' ,: ~d or -treated PTFE examples, for ~ , ' ' _ ' materials begi nning ionomer sol ids .v. ..~ t, <. liv"s i n the coating dispersion above 1 percent by weight do not yield appreciable , v . ,t.. These data also suggest that the 5 wt. percent sodium carbonate solution may preferably be used with the coated PTFE materials of these examplesratherthanthesodium.l~lv.ive ~ dsaltsolutionsemployedinearlierexamples.
Examples 57-76 Pul~t~llafl~v.v~ couponswerecoatedwithionomerfromdispersions havingvarioussolids~v.-~_.lt-aLio--.asinpreviousexamples,thenimmersedinoneofseveral saltsolutionsatambient , ._ e(25deg.qandapHof7Or12. Thesaltformionomers intheseexampleswereexchangedwithCa+2,Mg+2,Zn+2,K+orLi+,withsaltsolutionsbeing employed of the chloride salts of these cations or with a 26 weight percent sodium chloride salt solutionbeingused,followedbyconversiontotheparticularCa+2,Mg+2,Zn+2,K+orLi+
exchanged ionomers by soaking in 0.5 M solutions of the chloride salts of these cations for an hour. All specimenswererinsedand , "' _ ' inwaterbeforecontactangle were undertaken, and both annealed and unannealed specimenswere prepared and tested.

2~
Wo9s/24976 ~ .,. S.~ /
Theparticularsofspecimenspreparedford~....;..;,.~theeffectofCa~2onthe coated PTFE materials of the present invention, and the results therefrom, are as indicated in Table S:
Table 5 Contact Sample lonomer Salt Solution DH 9Dea) Dev'lation Annealed 1.00 NaCI 12 104.4 8.81 Annealed 1.00 NaCI 12 104.3 2.97 11 Unannealed 1.00 NaCI 12 66.5 3.52 Unannealed 0.50 NaCI 12 80.5 4.21 Unannealed 0.25 NaCI 12 82.1 6.40 Annealed 1.00 20%. CaCI2 7 109.2 2.89 Unannealed 1.00 20% CaC12 7 76.5 5.88 Those specimens associated with the study of Mg ~ 2 are described in Table 6, along with the results of the contact angle testing conducted thereon:
Tsble 6 Contact lonomer Angle (Avq., 5td.
Sample t. Pct.~ 5altSolution PH Dea~ Deviation Annealed 1.00 NaCI 12 113.4 10.78 25 Annealed 1.00 Nacl 12 93.1 9.21 Unannealed 1.00 NaCI 12 85.2 5.67 Unannealed 0.50 Naa 12 89.4 3A1 Unannealed 0.25 NaCI 12 87.4 4.23 Annealed 1.00 20% MgCI2 7 97.2 ~ 6.54 30 Unannealed 1.00 20% MgC12 7 84.3 3.67 ThosespecimensassociatedwithZn+2,K~andLi~aredescribedinTable7,along withtheresultsofthecontactanglewettabilitytestingconductedthereon:

Wo9~/24976 ~ 8~i~5i4 Table 7 Contact lonomer Salt Angle ~L Std.
SamDle/Cation (Wt Pct) Solution ~H Decl) Deviation 5A. -, ' ' 7'1 + 2 1.00 2096 ZnC12 7 89.3 3.55 U~ 7n + 2 1 .00 20% ZnC12 7 69.3 6.00 Annealed/K + 1.00 20% KCI 7 86.3 4.90 U--~---- ' "1~+ 1.00 20% KCI 7 84.5 7.96 Annealed/Li + 2 1.00 20% LiCI 7 121.0 9.95 Unannealed 1.00 20% LiCI 7 73.0 6.10 Theseexamplessuggestthatagooddegreeofflexibilityexiskinthesaltsoiution treatment step and in the appl ication ~ and the resulk with calci um and magnesiuminparticularsuggestthatthepresenceofthe#materialsinachlor-alkali e. . . :. ~,. . ,L should not prove adverse to the use of, for example, coated PTFE in such an ~...:.~,.
Example 77 Glass slides were cleaned by rinsing with acetone and deionized water, then air dried. Thecleanedslidffwerecoatedbyimmersionindispersions(in50vol.percent ethanol/50vol.percentwater)ofvarious.~ t.aLN,..,ofthe800equivalentweightionomer kodium salt, again) of previous examples. Excess ionomer dispersion was allowed to drain from the slides, and the slides immersed in a 25 weight Percent NaCI salt solution, rinsed with deionized water and air-dried.
The coati ngs produced on the sl ides i n this fashion were then analyzed for smoothnessandcoatingthicknessbyX-rayphotons~,__L-~"...py,withthesmoothnessbeing determinedbyscanningacrossthecoating'ssurfacewhilemeasuringtheatompercentof fluorineinthecoating. ThecoatingthicknesswasestimatedbyvaryingtheangleoftheX-ray photon~.__L.~ ",ybeamwhilemeasuringthesiliconesignalobservedthroughthecoating.
TheresulkareshowninTable8below. Forcomparison,thecalculatedatom percentoffluorineinapureanhydrous800equivalentweightionomerinsodiumsaltformis 64.4 percent.

Wo95/24976 ~1 ~ 55~ ".,~ 77 Table 8 lonomer Pct. Fluorine C~ elltl~livll Estim. Max.
Q~Min. Max Delta Thickness (nm)

5 û.25 48.0 55.0 7.0 4.0 0.50 56.0 61.0 5.0 6.0 J
1.00 58.0 60.0 2.0 8.5 3.00 40.0 57.0 17.0 5.00 12.0 58.0 46.0 (*) Coatingsweretoouneventoestimate.
A sub-micron coating is evidently achieved, and the data suggest thatthe inventiveprocesscanproducecoatingswhosethicknessapproachesthedimensionsofa Langmuir-Blodgett,~v..~,...~lo;ulll.fllm. Thethicknessanduniformityofthecoating producedbythisparticularprocessandwiththisparticularsolventandionomerappear optimumatanionomer.~ .-t. somewherebetweenO.5and3.0percentbyweightof the dispersion.
20 Example 78 In order to determine the percentage utilization of ionomer in a film coating producedbyaprocessofthepresentinventionfromadispersionofagiven.~,,..e..L,~.~i.anof ionomer in alcohol and water, glass slides (19 mm by 75 mm by 1 mm) were cleaned with ~cetone and water as in Example 77, and preweighed in a closed, clean widemouth jar.
Theseslideswerethenimmersedtoafixeddepthof60mminadispersionofa given .~ el L, u Li.sn of the same ionomer as used i n Example 77 and previous examples (thus providing a wetted area on each slide of 24.2 square ~ .). The slides were removed fromthedispersionsandallowedtodrainforlOseconds,andthentouchedtocleanglassslidesto remove excess, last drops of dispersion therefrom.
Thewettedslideswerethenplacedbackinthewidemouthjar,whichwasthen c~pped. Thejarandcoatedslidecontainedthereinwerethenreweighedforcomparisonto theobservedprecoatedweighttodeterminetheweightoftheliquidfilmoftheionomer solution. The potential coating thickness was calculated in each instance by assuming that all of the ionomer present in the liquid fllm was deposited as a uniform coating on the glass 35 surface. This calculated thickness was compared to the measured thickness from the previous example.
The reslllts hl~m ~histeltin ~ ~re shown in T~bl~ 9:

Wo9S/24976 ~ ; 5~ r~l,o~ 7 Table 9 Wt. of lonomer Potential Measured lonomer Pct.Ionomer Weight in lonomer lonomer Used in lonomer Soln. Soln. Thickness Thickness Coating (bv Wt.) (arams) (arams) (nm, max.) (nm. max.) (Pct.) 0.930.0642 5.97E-04 123 8.5 6.9 0.500.0581 2.90E-04 60 6.0 1 û.0 0.250.0576 1.44E-04 29 4.0 13.7 OnlyarelatiYelysmallproportionoftheiu,, ~ depositedontheslides from these dispersions. The excess ionomer can be rinsed away, and potentially recovered and recycled for forming additional coatings on various substrates.
ExamPle 79 A small piece of platinum foil (1 cm. square in area) was picked up by one edge using forceps, and immersed to about 2t3 of its height in a dispersion (in 50 vol. percent ethanolt50 vol . percent water) of 1 wt. percent of the 800 equivalent weight ,u~
sodiumsulfonateformionomeremployedinearlierexamples. Thefoilwasthenremovedand allowedtodrainfor10seconds. Thedropleftatthebottomoftheplatinumsquarewas 20 removed by touchi ng the foil square to the rim of the ba Ltle contai ni ng the dispersion, and the wetted foil was then fully immersed in a soiution of sodium bisulfate (20 wt. pct.) in water. The foil was gently rinsed in a boLtle of deionized water and then immersed in a dilute solution of SafranineONcationicdye. Thetreated2t30fthefoilabsorbedthedyeandremainedrose-coloredandwettedafterfurtherrinsingwithdeionizedwater. Theuntreahd(uncoated)1t3 25 of the foil remained shiny and was water-beaded ExamDles 80-89 CouponsofPTFEweresoakedin1,1,1-l~ "v_LI,<",c,thenrinsedwithacetone and deionized water. These were then immersed in the dispersion of Example 79, removed from the dispersion and al lowed to drain, ; l ~, then immersed i n a nitric acid sol ution 30 orinoneoftheaqueoussaltsolutionslistedbelowinTable1û. Afterbeingrinsedbyagitating inabeakeroffreshdeionizedwater,thesurfacewettabilityofthecouponswasassessed visually. If water formed a continuous film on the coupon without beading, the coupon was deemedwettable. ThecouponswerethenimmersedinadilutesolutionoftheSafranineON
dye,andthequalityofthecoatingsthereoncomparedbycomparingcoloruniformity('1~
35 being indicative of the most uniform color observed, and higher numbers suggesting Iffser degnes of uniformity). The results of these tests are shown in Table 10 as fol lows:

WO ssl24976 ~ r~ 77 Table l o Wt. Pct. Color Salt (in Water) Wettable? Uniformitv Sodium bisulfate 2û yes Nitric acid 70 yes Ammonium chloride 20 yes 1 ~, Sodium acetate 20 yff 2 T~L~yl ~ l iodide ca. 2.5 yes 3 Sodium chloride 25 yes 4 Potassium chloride 27 yes 5 Silver nitrate 20 yes 6 Ferric nitrate 18 yes 7 C~tylL,;,.. ~ ;.,.. chloride 25 yes NA
C~tyll,;... _;l,,' ,;umchloride 5 no NA
.;d;~;u~ chloride S no NA
The colors observed on these coupons ranged from a deep rose to a very pale pink,exceptthatthecoatingdepositedbythe25percentbyweight~.tyl~,i ",' .,;~
chloride was essentially colorless. This variation is considered as reflecting the ease of exchanqingthecationicdyeintothecoating. ThesampleimmeKedinnitricaciddevelopeda bluish tinge as it dried.
Withrespecttothesaltsolutions,theresultsinTable10suggestthatawide varietyof~ s~,lul,l~saltscanbeusedintheprocffsofthepresentinvention,buttheresults with the more ~on~. .t. ' and less .~,, I.el ,t, ~:~1 surface adive cetyl quaternary ammonium saltsalsosuggestthatthevarioususeful- ' ' '' saltsmayberequiredtobeemployedin different~ t~ llstooeeffectiveforformingasatisfactoryadherentcoatingonany given substrate.
Examples 90-91 A 0.92 weight percent dispersion of an ethylene-acrylic acid copolymer (containing20percentbyweightofacrylicacid))waspreparedbydiluting 1 partbyweightofa .-...._..' 'l~. " '' 25percentbyweightdispersionofsuchpolymer(soldasAdcote4983 EAA dispersion by Morton 1, .". " " . ' Inc., containing 25 weight percent solids neutralized withO.8equivalentsofammoniumhydroxideperequivalentofacid),with12.8partsbyweight of water and 13.3 parts by weight of ethanol . A PTFE coupon cleaned by acetone washing, W0 95/24976 ~ r~
deionized water rinsing and drying was immersed in part in the 0.92 per cent dispersion, the excess allowed to drain, the coated part immersed in a salt solution of 20 weight percent of sodiumbisulfateinwaterandthenwater-rinsed. Thetreatedportionofthecouponwas clearly . 1~ . ' After exposure to hfranine O'' dye, the treated portion showed a 5 conti nuous area of very pale pi nk.
A clean PTFE coupon was immersed for comparison in a 1.0 weight percent solids dispersioninwateralone(preparedbydiluting~.OgramsoftheAdcote4983~materialwith 23.4 grams of deionized water), and drained of excess dispersion. The surface of the coupon wasnotwettedbythedispersionexceptforafewisolateddrops,andwhenimmersedinthe 10 sodiumbisulfatesoiution,rinsedwithdeionizedwaterandimmersedindilutedSafranineO~
inwaterdisplayedonlyafewisolatedspotsofpink.o,-e,,uu"d;.-~generallytotheearlier-noted drops of dispersion.
The procedure with the 0.92 weight percent solution was also repeated with a cleanedpul~,,,~, ,'~ .ecoupon. Thetreatedareaofthecouponwasagainclearlywater-wetted,anddyeingwithSafranineO~dyegaveacontinuoustreatedareaofpalepink.
Examples 92-93 A sample of a sulfonated poiystyrene (such as is ~ available from Aldrich Chemical Co., Inc.) containing 1 milliequivalent of acid groups per gram of polymer was dissolved in anhydrous dioxane to give a 1.1 weight percent sol ution of the sulfonated 20 polystyrene- An ac~ t ~ ' d, water-rinsed and dried PTFE coupon was i mmersed i n part in the suifonated polystyrene solution and allowed to drain. A continuous film was not formed, andafterimmersionina20wt.percentsolutionofsodiumbisulfateinwateranddyeingwith Safranine O~ dye, only isolated areas of the coupon were observed to have been coated and dyed.
A second sulfonated polystyrene solution was then prepared containing 1.2 wt.
percent of the sulfonated polystyrene in a mixture of U weight percent dioxane with 52 weight percent of water, with the sulfonated polystyrene fir!it being dissolved in the dioxane ~nd then diluting with water. A cleaned PTFE coupon immersed in part in this solution showed a continuous film of the solution on the PTFE coupon surface. The wetted coupon portion was 30 immersed i n the same sodium bisulfate salt sol ution, and a r~. . i ;. ,;;. .cJ was . ..
in a continuous film. After being dyed with Safranine O~ dye, a continuous rose-colored area was observed with some variation in the shade being seen as well.
A pul~ e cou pon was coated by the same procedure, and yielded a - translucent, continuous water-wetted area which was a deep rose co~or on dyeing with the 35 Safranine O~ dye.
Examples 94-1 00 An800equivalentweight;v.-u,~.~. . preparedby~u,~,vl~ aLi~llOf CF2 = CF2 with CF2 = CFOCF2502F in an emulsion ,~,ul~ i.ali~n system. The resulting polymer ,, _ _ . ,,, _,, _ ,, . . , _,, . ,,, _, _ . , . ,,,,, , _ _

6 ~ 5~
was isolated and dried, and hydrolyzed with NaOH to give a ,u_. r~ " i ' sodium sulfonate form ionomer. After being water-washed to neutrality, the ;~ converted to the acid (H ~) form by exposure to l ,, ' ~ -1,;~" ic acid. After again being ~ ;1 to neutrality and air-dried,theionomerwaschargedwithwateronlytoa300mLstirredParrbombreactor. The 5 vesselwasclosed,andheatedtoaselectedtemperaturewithstirringforabout2hourswhilemonitoringthesystempressure. Aftercoolingtoambient; , _ ~.,theamountof ~onomer in the d ispersion (and from this, the yield of ionomer in the dispersion) was determinedbydrawingoffa15to20gramsampleoftheliquid.~,.""~ili.,n,~ to dryness and weighing the residue. The resulk are shown in Table 11:
Table 1 1 P,inPsia Wt%
onomer,~gl Water(a) (MPa) Temp(C) lonomer Yield(%) 6.2200 230-240 (1 .6- 200 2.74 92 1.n 2.28 72.89 162 (1.1) 185 2.68 89 2.35 76.04 163(1.1) 185 2.68 89 2.31 74.93 163 (1.1) 185 2.63 88 2.21 71.46 145-163(1.0- 180-185 2.84 95 1 .1) 5.75 200.4 480-490 (3.3- 240 2.67 93 3.4) 6.2(a) 200 230-240 (1.6- 200 2.21 80 1.7) (a) Film form, all others being powders;

Example 101 Intoa50gallon(191iter)vesselwereplaced292pounds(133kg)ofwaterand9 pounds(4kg)oftheionomeremployedinExamples94-100,theionomerhavingbeen convertedasapowdertoitsacidform. Thevesselwasclosedandheatedat180to185degrees 30 Celsiusfor2hourswhilestirring. Thepressurewas130psig(0.9MPa). Aftercooling,the amount of polymer in the liquid phase was determined by evaporating a 15-20 gram sample to dryness and weighing the residue. The measured yield was 92 percent.

W0 9S124976 ~ 1 8 ~ ~ ~ 4 P~
Examrle 1Q2 Thesamevessel,ionomerandprocedurewereusedasinExample 101,with3 pounds(1.4kg)ofionomerand 160pounds(73kg)ofwaterbeingchargedtothevessel. The temperatureofthistrialwas180degreesCelsius,andthemeasuredpressurereached110psig 5 (0.8MPa). Themeasuredyieldundertheseconditionswas98percent.
ExamPle 103 About75pounds(34kg)ofTeflon~7CPTFEpowderand225pounds(102kg)of waterweremixedatatipspeedof6,600ftJmin.(2030 ~ for15minutes,ina CowlesHLM5eries~sin9leshaftmounthighsheardissolver(r~ el.v~ Cowleslnc.,Fullerton, 10 CaliforniaUSA)equippedwitha6inch(15cm.)diameterhigh-shearimpeller,to,u,~
PTFEpowderto llumvy_.~_ Ly.
After removing about 65 pounds (29.5 kg) of water, and while stirring at a tip speed of 4,350 ft~min. (1340 ...~ ` 40 pounds (18 kg.) of a 2.75 weight percent dispersion of the 800 equivalent weight acid form ionomer of previous examples were added.
Afterstirringfor10minutes,auniformslurrywasobtained. About21 pounds(9.5kg)ofdry sodium chloride and 4.5 pounds (2 kg) of 50 pct NaOH were added to the slurry, and mixing wascontinuedforanothertenminutes. Al _ ~v~slurrywasobtainedwithweLted~
ionomer-coated PTFE.
Example 104 Forthisexample,45gramsofanacidfomm,shortersidechainionomerofthetype usedinExamples94-100above,buthavinganequivalentweightof98û,wasplacedinavessel with 1400 grams of water. The vessel was closed, and the . '~ mixture heated with stirringto196degreesCelsiusandapressureof189psig(1.3MPa,gauge)fortwohours, Aftercoolingand~., aLi..yaportiontodrynessinthemannerofExamples94-100,thesolids 25 content of the dispersion was detenmined to be 2.82 percent by weight for a yield of from 94 to 95percent(takingintoaccountthatthe~,ol~ .. addedtothevesselwasnotcompletely dried) .

Claims (13)

Claims:

1. A process for coating an ion-containing polymer onto a selected substrate, which comprises:
contacting the substrate with a colloidal dispersion or solution of the ion-containing polymer; and then contacting the dispersion- or solution-wetted substrate, while still wetted withthe colloidal dispersion or solution and without an intervening drying step, with a solution of a salt or of a strongly ionizing acid of a sufficient concentration to cause an adherent coating of the ion-containing polymer to be formed on the substrate.

2. A process as defined in Claim 1, further comprising contacting the coated substrate with a solution containing a different cation, so that a different cation-exchanged form of the coated ion-containing polymer results.

3. A process as defined in Claim 1 or as defined in Claim 2, further comprising heat treating the coated substrate at an elevated temperature, then contacting the heat-treated, coated substrate with a colloidal dispersion or solution of an ion-containing polymer and contacting the thus-wetted substrate with a solution of a salt or of a strongly ionizing acid of a sufficient concentration to cause a second coating of ion-containing polymer to be formed on the substrate.

4. A process as defined in any one of Claims 1-3, which further comprises annealing the coated substrate at the glass transition temperature of the ionomer or greater.

5. A process as defined in Claim 4, wherein the substrate is polymeric in nature and further, wherein the annealing of the coated substrate occurs at the crystalline melting point of the polymeric substrate.

6. A process as defined in any one of Claims 1-5, wherein a sulfonated polystyrene, a copolymer of a non-acid, ethylenically unsaturated monomer with an ethylenically unsaturated carboxylic monomer, or a perfluorocarbon ionomer is employed in a colloidal dispersion or solution for forming a coating on the substrate.

7. A process as defined in Claim 6, wherein a perfluorosulfonic acid ionomer is employed as represented by or by , or which is an alkali metal-exchanged salt of one of these perfluorosulfonic acid ionomers.

8. A process as defined in any of Claims 1-7, wherein a colloidal dispersion or solution is employed for forming a coating on the substrate which when brought into contact with the substrate does not contain any solvent or any liquid medium other than water.

9. A process as defined in any of Claims 1-8, wherein the substrate is in the form of a fiber, powder, fabric or article of polytetrafluoroethylene, polyvinylidene fluoride, a fluorinated ethylene-propylene copolymer, poly(vinyl chloride), glass, polypropylene, carbon, steel, platinum, chlorotrifluoroethylene or a perfluoroalkoxyvinyl ether-tetrafluoroethylene copolymer.

10. A process as defined in Claim 8, wherein:
the substrate is polytetrafluoroethylene, polyvinylidene fluoride, poly(vinyl chloride), polypropylene, a fluorinated ethylene-propylene copolymer, chlorotrifluoroethylene or a perfluoroalkoxyvinyl ether-tetrafluoroethylene copolymer and is in the form of a powder, fibers or a mixture of powder and fibers; and contacting the substrate with the colloidal dispersion or solution involves adding the dispersion to the substrate and subjecting the mixture to high shear conditions.

11. A process as defined in Claim 10, wherein the solventless dispersion or solution is formed of a perfluorosulfonic acid ionomer of the formula and having an equivalent weight of from 550 to 1000, the ionomer solids are combined with the substrate in a ratio by weight of 0.015 to 1 or greater, and the shearing of the mixture is accomplished with a blade on a blending device at a tip speed of 240 meters per minute or greater.

12. A process as defined in Claim 11, wherein the perfluorosulfonic acid ionomer has an equivalent weight of from 550 to 800.

13. A process as defined in any one of Claims 10-12, wherein the substrate is polytetrafluoroethylene.